object

Using the knowledge you have learned, describe the person in your mind

Var mrDeng = {name: "mrDeng", age: 40, sex: "male", health: 100,// can change in console smoke: function () { console.log('I am smoking'); mrDeng.health --; }, drink : function () { console.log('I am drink'); mrDeng.health ++; }}Copy the code

Improve the first person: this

Var mrDeng = {name: "mrDeng", age: 40, sex: "male", health: 100,// function () { console.log('I am smoking'); this.health --; }, drink : function () { console.log('I am drink'); this.health ++; }}Copy the code

1. Add, delete, modify and search attributes

increase

drink:function(){
    console.log('I am drinking');
    this.health ++;
}
meDeng.wife = "xiaowang";
// console.log(mrDeng.wife = "xiaoliu");
// console.log(mrDeng);
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change

console.log(mrDeng);
console.log(mrDeng.sex = "male");
console.log(mrDeng.sex);
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Delete The delete + attribute

When a variable is not declared, an error is reported. If an object property is not declared, it will print undefined

var deng = { prepareWife : "xiaowang", name : "laodeng", sex : "male", gf : "xiaoliu", wife : "", divorce : function () { delete this.wife; this.gf = this.PrepareWife; }, getMarried : function () { this.wife = this.gf; }, changePrepareWife : function (someone){ this.PrepareWife = someone; }}Copy the code

2. Object creation method

1. Var obj = {} is called plainObject

2. Constructor

(1) The system’s own constructor new Object

var obj = new Object();
obj.name = 'abc';
obj.sex = 'female';
obj.say = function(){
}
var obj = {
    name : ""
}
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System-provided: new Object(); Array(); Number(); Boolean(); Date();

(2) Custom

Function Car(){this.name = "BMW"; this.name = "BMW"; this.name = "BMW"; this.height = "1400"; this.lang = "4900"; this.weight = 1000; this.health = 100; this.run = function (){ this.health --; } } var car = new Car(); Var car1 = new Car(); // Not one person, not console. Log (car.run()); console.log(car1.health); console.log(car.health);Copy the code

demo

Achieve their own matching color

function Car(color){
    this.color = color;
    this.name = "BMW";
    this.height = "1400";
    this.lang = "4900";
    this.weight = 1000;
    this.health = 100;
    this.run = function (){
        this.health --;
    }
}
var car = new Car('red');
var car1 = new Car('green');
console.log(car/car1);
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function Student(name,age,sex) {
    this.name = name;
    this.age = age;
    this.sex = sex;
    this.grade = 2017;
}
var student = new Student('zhangsan',18,'male');
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Matters needing attention

var obj = new Object(){
    obj.name = 'abc';
    obj.sex = 'female';
    obj.say = function(){
    }
}
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Var obj = {name: ""// colon}Copy the code

The inner workings of constructors

There are three steps that happen with new

1. Implicitly add var this = {} 2 to the body of the function. Execute this. XXX = XXX; 3. Implicitly return this

function Student(name,age,sex) {
    //var this = {
    // name : ""
    // age : 
    // };
    this.name = name;
    this.age = age;
    this.sex = sex;
    this.grade = 2017;
    // return this;
}
var student = new Student('zhangsan',18,'male');
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function Person(name, height){
    // var this = {}
    this.name = name;
    this.height = height;
    this.say = function (){
        console.log(this.say);
    }
    // return this;
}
console.log(new Person('xiaoliu',180).name);
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Simulated constructor

function Person(name, height){
    var that = {};
    that.name = name;
    that.height = height;
    return that;
}
var person = new Person('xiaowang', 180);
var person1 = new Person('xiaozhang',175);
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trivia

function Person(name, height){ var this = {}; this.name = name; this.height = height; this.say = function (){ console.log(this.say); } return {}; Return this; // return this; } var person = new Person('xiaowang', 180); var person1 = new Person('xiaozhang',175); // But return a raw value is not allowedCopy the code

Object. Create (prototype) method

A wrapper class

1. The little knowledge

Primitive values cannot have properties and methods. Only objects can have properties, including objects themselves, arrays, and functions. Numbers are not necessarily raw values. There are two kinds of numbers: raw values Numbers are raw values. There are two kinds of numbers and strings. var num = 123; Var num = new number(123); Also a number, object 123

console.log(num); console.log(num.abc='a'); console.log(num.abc); console.log(num); console.log(num*2); // Become a number, no object attributes, same as string, BooleanCopy the code

Cannot have two original values of an attribute: undefined null

String(); Boolean(); Number();

var num = new Number(123); var str = new String('abcd'); var bol = new Boolean('true'); // undefined and null cannot have properties console.log(num.abc);Copy the code

2. The phenomenon:

Var STR = "abcd"; str.length = 4; Str.abc = 'a'; str.abc = undefined;Copy the code

The original value cannot have properties and methods because it goes through the process of wrapping the class before it can be called

var num = 4; // Wrapping class console.log(num.len = 3); //new Number(4).len = 3; delete // new Number(4).len console.len(num.len); //undefined // num does not have lengthCopy the code

Examination questions

It’s based on a theory: array truncation

var arr = [a,b,c,d];
console.log(arr.length = 2);
console.log(arr);
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Into the elder brother of bo

var str = "abcd"; str.length = 2; // new String('abcd').length = 2; delete console.log(str); //abcdCopy the code

variant

var str = "abcd"; str.length = 2; // new String('abcd').length = 2; delete // new String('abcd').length console.log(str.length); / / 4Copy the code

prototype

Definition 1.

A stereotype is a property of the Function object that defines the common ancestor of the object produced by the constructor. Objects generated by this constructor can inherit the properties and methods of the stereotype. Prototypes are also objects.

The constructor produces an object:

// Person. Prototype = {} Person. Prototype name = "hehe"; function Person() { } var person = new Person();Copy the code

Application:

Example 1: Take what you own

Person.prototype.LastName = "Deng"; Person.prototype.say = function(){ console.log('hehe'); } function Person() { // this.LastName = 'ji'; } var person = new person (); var person1 = new Person();Copy the code

Example 2:

Person.prototype.LastName = "Deng";
Person.prototype.say  = function(){
    console.log('hehe');
}
function Person(name,age,sex) {
    this.name = name;
    this.age = age;
    this.sex = sex;
}
var person = new Person('xuming',30,'male');
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2. Extract common attributes.

function Car(color,owner) { this.owner = owner; this.carName = "BMW"; // This. Height = 1400; this.lang = 8900; this.color = color; } var car = new Car('red','prof.ji');Copy the code

To optimize the

Car.prototype.height = 1400;
Car.prototype.lang = 8900;
Car.prototype.carName = "BMW";
function Car(color,owner) {
    this.owner = owner;
    this.color = color;
}
var car = new Car('red','prof.ji');
var car1 = new Car('green','laodeng');
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3. Add, delete, change and check the original form

increase

Person.prototype.lastName = "Deng"; / / shape properties have changed, want to change, is going to call the Person. Prototyoe. LastName function Person (name) {enclosing name = name; } var person = new Person('xuming');Copy the code

console.log(person.lastName="james"); // This is not called modification, this is called adding console.log(person); console.log(person.lastName);Copy the code

delete

console.log(delete person.name); console.log(person.name); console.log(delete person.lastName); console.log(person.lastName); // Delete invalidCopy the code

To optimize the

Car.prototype.height = 1400; Car.prototype.lang = 8900; Car.prototype.carName = "BMW"; Car. Prototype = {height: 1400, lang: 4900, carName: "BMW"}Copy the code

change

2. How does the object view the object’s constructor — > constructor

Function Person(){// constructor: constructor = {constructor: Person } function Car(){ } var car = new Car(); console.log(car.constructor);Copy the code

check

How do objects view stereotypes – > implicit property proto

function Person(){ } var person = new Person(); // Light purple, implicit naming rule console.log(person);Copy the code

person.prototype.name = 'abc'; function Person(){ } var person = new Person(); // Private attributes: var __pravite console.log(person.__proto__)//__proto__ contains the original formCopy the code

Person.prototype.name = 'abc'; function Person(){ var this = { // __proto__: Person. Prototype}} var perosn = new Person(); console.log(perosn.name);Copy the code

Changing the proto pointer causes the pointer to change

Person.prototype.name = 'abc'; function Person() { // var this = { // // __proto__: Person.prototype // } } var obj = { name: "sunny" } var person = new Person(); Person.__proto__ = obj;Copy the code

Demo 1

Person.prototype.name = "sunny"; function Person() { } var person = new Person(); Person.prototype.name = "cherry"; person.name; Prototype: Sunny, cherry, cherryCopy the code

Demo 2

Person.prototype.name = "sunny"; function Person() { } Person.prototype.name = "cherry"; var person = new Person(); console.log(person.name); CherryCopy the code

Demo 3

Person.prototype.name = "sunny"; function Person() { } var person = new Person(); Person.prototype = { name : "cherry" } person.name; Sunny. The original value is changed on the basis of the original, this time is the original shape changed, for a new objectCopy the code

Simplification: Cross-assignment of reference values

var obj = {name : "a"};
var obj1 = obj;
obj = {name : "b"};
obj1:a,obj:b     
Copy the code

Person.Prototype.name = "sunny"; Function Person() {//var this = {__proto__:Person. Prototype}}// var Person = new Person(); Person. Prototype = {name: 'cherry'} // prototype = {name:"a"}; // __proto__ = Person.Prototype; // Person.Prototype = {name:"b"};Copy the code

Demonstrate 4

Person.prototype.name = "sunny"; function Person() { } Person.prototype = { name: "cherry" } var person = new Person(); person.name; Answer: Cherry Function Person() {var this = __proto__ person.prototype} function Person() {var this = __proto__ person.prototype} Re - access: cover the followingCopy the code

Prototype chain introduction

Grand.prototype.LastName = "Deng"; function Gand(){ } var grand = new Grand(); Father.prototype = grand; function Father(){ this.name = "xuming"; } var father = new Father(); Son.prototype = father; function Son(){ this.hobbit = "somke"; } var son = new Son(); console.log(son.hobbit); console.log(son.name); // Follow the chain to console.log(son.tostring); Grand.proto__ = object. prototype Console. log(object.prototype); console.log(Object.prototype.__proto__); Proto is gone, so is the terminalCopy the code

Prototype chain

How to form a prototype chain?

1. Add, delete, modify and check the attributes on the prototype chain

Add, delete, modify: only I have permission, descendants did not

console.log(delete Father.prototype.n); / / deleteCopy the code

Special case: reference value call modification

var grand = new Grand();
Father.prototype = grand;
function Father() {
    this.name = 'xuming';
    this.fortune = {
        card1 : 'visa'
    }
}
var father = new Father();
Son.prototype = father;
function Son(){
    this.hobbit = "somoke";
}
var son =  new Son();
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console.log(son.fortune);
son.fortune = 200;
console.log(son);
console.log(father.fortune);
son.fortune.card2 = 'master';
cons.log(father);
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demo

Grand.prototype.LastName = "Deng";
function Grand(){

}
var grand = new Grand();
Father.prototype = grand;
function Father(){
    this.name = "xuming";
    this.forture = {
        card1 : 'visa'
    };
    this.num = 100;
}
var father = new Father();
Son.prototype = father;
function Son(){
    this.hobbit = "smoke";
}
var son = new Son();
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console.log(son.num++); 100 console.log(father); 100 console.log(son.num); 101Copy the code

demo

Person.prototype = { name : "a", sayName : function(){ console.log(this.name); } } function Person(){ } var person = new Person(); // ACopy the code

Person.prototype = {
    name : "a",
    sayName : function(){
        console.log(this.name);
    }
}
function Person(){
    this.name = "b";
}
var person = new Person();
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Person.sayname (); a.sayname (); person.sayname (); Person called, b if person.prototype.sayname (); a

Person.prototype = {
    height : 100
}
function Person(){
    this.eat = function(){
        this.height ++;
    }
}
var person = new Person();
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console.log(person.eat); person.eat(); console.log(person.eat); // Default return: undefined to view the code to writeCopy the code

Company specification: Arrays, objects are created with literals

var obj = {}; Var obj1 = new Object(); var obj1 = new Object(); Var obj = {}; We have a new Object() inside, so we write the Object literalCopy the code

Most objects eventually inherit from Object.prototype

(选题真题) exception: because object.create

console.log(Object.create()); Console. log(object.create (null));Copy the code

Object. Create can also create objects

// var obj = Object; var obj = {name : "sunny", age : 123}; var obj1 = Object.create(obj); // Obj1 becomes the object. The original form of obj1 is obj, so obj1.name is obj.nameCopy the code

Person.prototype.name = "sunny";
function Person() {
}
var person = Object.create(Person.prototype);
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2. About the toString:

Only undefined and null cannot call toString numbers because 123.toString() is accessed layer by layer through the wrapper class; Undefined has no wrapper class and is a primitive value that cannot be called

console.log(undefined.toString); console.log(null.toString); obj.__proto__ = { name: sunny}; console.log(obj.name); // It doesn't workCopy the code

ToString returns different returns for each variable and each attribute value

var num = 123; console.log(num.toString); // string console.log(123.tostring); // identify the float typeCopy the code

The phenomenon of

var obj = {}; obj.toString(); ---->[object Object]Copy the code

why

var num = 123; // num.toString(); -->new Number(num).toString(); Number.prototype.toString = function (){ } // Number.prototype.__proto__ = Object.prototypeCopy the code

Rewrite pen test: write a method rewrite form, write a system with the same name, different functions

// Object.prototype.toString = function (){
// } 
Person.prototype = {
    toString : function () {
        return 'hehhe';
    }
}
function Person () {
}
var Person = new Person();
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3. The little bug

The console. The log (0.4 * 100); //js accuracy is not console.log(math.ceil (123.234)); // round up console.log(math.floor (123.99999)); / /Copy the code

Randomly generate 0-100 random numbers

Math.random(); For (var I = 0; i < 10; i++){ var num = Math.random().toFixed(2)*100; console.log(num); // there will be a deviation}Copy the code

Solution: first *100 and then round

for(var i = 0; i < 10; i++){ var num = Math.floor(Math.random() * 100); console.log(num); } // Summary: the normal calculation range: 16 before and 16 after the decimal pointCopy the code

call/apply `Forbid to`

1.call

Function to change the this pointer. Borrow other people’s function to achieve their own function distinction, the form of parameters passed behind different. Call needs to pass arguments as many arguments as the parameters apply needs to pass arguments

function test(){ } test()===test.call(); // The default is implicitCopy the code

You can pass things in call

function Person(name, age){ this.name = name; this.age = age } var person = new Person('deng',100); var obj = { } // Person.call(obj); Person.call(obj,'cheng',300); Person.call(obj,'cheng',300);Copy the code

Enterprise development

Function Person(name, age, sex) {this.name = name; function Person(name, age, sex) {this.name = name; this.age = age; this.sex = sex; } function Student(name, age, sex, tel, grade){ this.name = name; this.age = age; this.sex = sex; this.tel = tel; this.grade = grade; Function Person(name, age, sex) {this.name = name; this.age = age; this.sex = sex; } function Student(name, age, sex, tel, grade){ // var this = {name : "", age : "",sex : ""} Person.call(this, name, age, sex); this.tel = tel; this.grade = grade; } var student = new student ('sunny',123,'male',139,2017);Copy the code

Building cars, for example,

function Wheel(wheelSize,style) { this.style = style; this.wheelSize = wheelSize; } function Sit(c,sitColor) { this.c = c; this.sitColor = sitColor; } function Model(height,width,len) { this.height = height; this.width = width; this.len = len; } function Car(wheelSize, style, c, sitColor, height, width, len) { Wheel.call(this, wheelSize,style); Sit.call(this,c,sitColor); Model.call(this, height, width, len); } var car = new car (100,' black ','red',1800,1900,4900);Copy the code

2. Apply:

Apply can only pass an array of arguments wheel. apply(this, [wheelSize,style]);

Conclusion:

Call: The argument needs to be passed in according to the number of parameters

Apply: Need to pass a arguments

Assignment: Ebook JS design patterns on pages 0-35

Pen try: use friend 2017 school recruit front end

Succession history

1. Traditional form

Too many inherited useless attributes

Grand.prototype.lastName = "Ji"; function Grand() { } var grand = new Grand(); Father.prototype = grand; function Father() { this.name = "hehe"; } var father = new Father(); Son.prototype = father; function Son() { } var son = new Son(); // a series of succession from beginning to end, resulting in the succession of those who do not want to continueCopy the code

2. Borrow constructors

You can’t inherit a prototype that borrows a constructor that takes one more function each time it actually wastes efficiency

function Person(name,age,sex){ this.name = name; this.age = age; this.sex = sex; } function Student(name, age,sex, grade) {Person. Call (this,name,age,sex); this.grade = grade; } var student = new Student();Copy the code

3. Share prototypes

You can’t just change your prototype

Father.prototype.lastName = "Deng"; Function Father(){// Father(){function Son(){}Copy the code

Implementation method

Prototype chain

Var father = function Son(); 4. 0. How to Lose weight

Father.prototype.lastName = "Deng";
function Father() {
}
function Son() {
}
Son.prototype = Father.prototype
var son = new Son();
var father = new Father();
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Abstracted as a function

Father.prototype.lastName = "Deng"; function Father() { } function Son() { } function inherit(Target, Origin) { Target.prototype = Origin.prototype; } inherit(Son, Father); var son = new Son(); //son.LastName = "Deng";Copy the code

To inherit before using, son.lastname refers to the original space

Father.prototype.lastName = "Deng"; function Father() { } function Son() { } function inherit(Target, Origin) { Target.prototype = Origin.prototype; } var son = new Son(); inherit(Son, Father); Son. lastName = undefinedCopy the code

Inadequate:

Son adds an attribute to himself, which is convenient for the subsequent production of the object to use. It can not be personalized implementation, inheritance, but impact

Father.prototype.lastName = "Deng"; function Father(){ } function Son(){ } function inherit(Target, Origin){ Target.prototype = Origin.prototype; } inherit(Son, Father); Son.prototype.sex = "male"; Var son = new son (); var son = new son (); var father = new Father(); // To achieve: want to inherit but not influence each otherCopy the code

4. Holy Grail mode

Through the prototype chain

function inherit(Target, Origin) {
    function F(){};
    F.prototype = Origin.prototype;
    Target.prototype = new F();
}
Father.prototype.lastName = "Deng";
function Father(){

}
function Son() {

}
inherit(Son,Father);
var son = new Son;
var father = new Father();
console.log(Son.prototype.sex = "male");
console.log(son.sex);
console.log(father.sex);
console.log(Father.prototype);
Copy the code

Constructor should point to the constructor, however, son.constructor = ƒ Father()？？？？ What’s going on?

The system has a built-in property called constructor, which by default points to its constructor

Son. __proto__ - > new F (.) __proto__ - > Father. The prototype / / points to the disorderCopy the code

Achieve inheritance: Must have the Holy Grail mode

function inherit(Target, Origin){ function F(){}; F.prototype = Origin.prototype; Target.prototype = new F(); Target.prototype.constructor = Target; Target.prototype.uber = Origin.prototype; / / super parent: super class} Father. The prototype. The lastName = "Deng"; function Father(){ } function Son(){ } inherit(Son, Father); var son = new Son(); var father = new Father();Copy the code

Upside down

F.prototype = Origin.prototype; Target.prototype = new F(); // Do not reverse, must change the original shape before newCopy the code

Kind of yahoo!

What closures do: Encapsulate and privatize properties

function Deng(name, wife){
    var prepareWife = "xiaozhang";
    this.name = name;
    this.wife = wife;
    this.divorce = function(){
        this.wife = prepareWife;
    }
    this.changePrepareWife = function(target){
        prepareWife = target;
    }
    this.sayPreparewife = function(){
        console.log(prepareWife);
    }
}
var deng = new Deng('deng','xiaoliu');
Copy the code

console.log(deng.sayPreparewife()); Console. log(deng.preparewife)// If you can't see it directly, privatize the variableCopy the code

F becomes the privatization variable

var inherit = (function(){ var F = function(){}; Return function(Target,Origin){f.protoType = origine.prototype; Target.prototype = new F(); Target.prototype.constuctor = Target; Target.prototype.uber = Origin.prototype; }} ());Copy the code

Discrete Mathematics (important) — >CS majors (Computer majors) ，，，， Probability theory, artificial Intelligence

The namespace

Is the object

Manage variables, prevent global pollution, suitable for modular development

One page, multiple people collaborate, merge conflicts

1. The old way: namespaces

var org = {
    department1 : {
        jicheng : {
            name : "abc";
            age : 123;
        },
        xuming : {

        }
    },
    department2 : {
        zhangsan : {

        },
        lisi : {

        }
    }
}
var jicheng = org.department1.jicheng;
jicheng.name;
Copy the code

2. New approach: Privatize variables with closures

webpack

Closure (privatize variables) + execute the function immediately

var name = "bac";
var init = (function(){
    var name = "abc";
    function callName(){
        console.log(name);
    }
    return function(){
        callName();
    }
}())
init();
Copy the code

Collaboration is not in conflict

var name = "bac";
var init = (function(){
    var name = "abc";
    function callName(){
        console.log(name);
    }
    return function(){
        callName();
    }
}())
var initDeng = (function(){
    var name = 123;
    function callName(){
        console.log(name);
    }
    return function(){
        callName();
    }
}())
Copy the code

Obj.eat ().smoke().drink().eat().sleep();

$('div').css('background-color','red').width(100).height(100).
html(123).css('position','absolute').
css('left','100px').css('top','100px');
Copy the code

Simulate jQuery to implement continuous call methods

var deng = { smoke : function () { console.log('Smoking... xuan cool!!! '); }, drink : function () { console.log('Drinking... good'); }, perm : function(){ console.log('perming... cool'); } } deng.smoke(); deng.drink(); deng.perm(); // How to implement JQ like continuous callCopy the code

Why not call it continuously

console.log('Smoking... xuan cool!!! '); // return undefined;Copy the code

Var deng = {smoke: function () {console.log(‘Smoking… xuan cool!!! ‘); return this; }, drink : function () { console.log(‘Drinking… good’); return this; }, perm : function(){ console.log(‘perming… cool’); return this; } } deng.smoke().drink().perm().smoke().drink();

Num = num; num = numCopy the code

var deng = { wife1 : {name : “xiaoliu”}, wife2 : {name : “xiaozhang”}, wife3 : {name : “xiaowang”}, wife4 : {name : “xiaoli”}, sayWife : function(num) { switch(num) { case 1: return this.wife1; }}}

Simplify the above code: concatenate variable attribute namesCopy the code

var obj = { name : “abc” }

**obj.name---->obj['name']; ** will be converted to square brackets inside, so so square brackets can be string concatenationCopy the code

Loop data group traversal: want to know the information of ten people, know one by oneCopy the code

Var arr =,3,3,4,5,6,7,8,9 [1]; Enumeration for(var I = 0; i < arr.length; i++){ console.log(arr[i]); / / traverse}

What if you want to find (traverse) the object?Copy the code

var obj = { name : “123”, age : 123, sex : “male”, height : 180, weight : 75 //prop:123 } for(var prop in obj){ console.log(obj.prop); // obj. Prop –>obj[‘prop’] is a property}

Truth:Copy the code

var obj = { name : ’13’, age : 123, sex : “male”, height : 180, weight : 178, proto : { lastName : ————hasOwnProperty}} for(var prop in obj) {console.log(obj[prop]); //console.log(obj[‘prop’]); // Obj. Prop is the same as obj.

Implementation of obj1 property +1 returns error demonstrationCopy the code

var obj1 = { a : 123, b : 234, c : 456 } var key; For (key in obj1) {obj1.key ++; }

## 1. HasOwnProperty () {hasOwnProperty () {hasOwnProperty ()Copy the code

var obj = { name : ’13’, age : 123, sex : “male”, height : 180, weight : 178, proto : { lastName : “deng” } } for(var prop in obj) { if(obj.hasOwnProperty(prop)){ console.log(obj[prop]); }}

Their set must be able to print, the system set must notCopy the code

var obj = { name : ’13’, age : 123, sex : “male”, height : 180, weight : 178, proto : { lastName : “deng”, proto : Object. Prototype // Once extended to the top of the prototype chain, the top will not be printed}}

## 2.in is similar to hasOwnPropertyCopy the code

var obj = { name : ’13’, age : 123, sex : “male”, height : 180, weight : 178, proto : { lastName : Log (‘height’ in obj)//height is called console.log(‘height’ in obj concole.log(‘lastName’ in obj)

HasOwnProperty () : hasOwnProperty () : hasOwnProperty () : hasOwnProperty () : hasOwnPropertyCopy the code

function Person(){ } var person = new Person(); var obj = {}; // A is the console.log(person instanceof person) constructed by the B constructor; // —->ture

See if there is A prototype of B on the prototype chain of object A (key point)Copy the code

console.log(person instanceof Object); —->ture console.log([] instanceof Array); —->ture console.log([] instanceof Object); —->ture console.log(person instanceof Array); —->false console.log(obj instanceof Person); —->false

Problem solved > Determine whether a variable is an array or an objectCopy the code

Typeof ([]) “object” typeof ({}) “object” / / demand: var arr = [] | | {};

The first method:Copy the code

var obj = {}; //var obj = []; Obj. Constructor //

The second method:Copy the code

[] instanceof Array //true var obj = {}; obj instanceof Array //false

The third method: toStringCopy the code

Object.prototype.toString.call([]); / / Object. The prototype. ToString = function () {/ / who calls, this is who / / identify this: / / / / return the corresponding results} / / obj. The toString (); // call.toString(); Object.prototype.toString.call([]); / / array can replace this Object. The prototype. ToString. Call (123); Object.prototype.toString.call({}); // Distinguish between arrays and objects

Console verificationCopy the code

Object.prototype.toString.call([]); “[object Array]” Object.prototype.toString.call({}) “[object Object]” Object.prototype.toString.call(123); “[object Number]”

# this ## 1. This -- > windowCopy the code

validationCopy the code

function test(){ console.log(this); } test();

## 2. This -- > window in the global scopeCopy the code

console.log(window);

Call /apply can change this to refer to ## 4.obj.f(); This in f() refers to obj). This refers to whoever calls this method. If no one calls this method, this is the windowCopy the code

Var obj = {a: function () {console.log(this.name)}, name: ‘ABC’} obj (); / / obj calls

## 5. The condition is false: 0, false, null, undefined, undefined. The function declaration is written in the operator, which is true, but the function declaration placed in the operator is not found at execution time. In addition, typeof for undeclared variables does not return an error, and undefined this is returnedCopy the code


# arguments

> arguments.callee

> func.caller

arguments

Copy the code

function test(){ console.log(arguments.callee); } test(); // Return its own function body

Application:Copy the code

var num = (function(n){ if(n == 1) { return 1; } return n* factorial (n-1); } (100))

Perform the factorial of a function immediately: can only be done with CalleeCopy the code

var num = (function(n){ if(n == 1) { return 1; } return n*arguments.callee(n-1); } (100))

Inside that function, it prints whateverCopy the code

function test(){ console.log(arguments.callee); function demo(){ console.log(arguments.callee); } demo(); }

Caller: In which environment is demo invokedCopy the code

function test () { demo(); } function demo() { console.log(demo.caller); } test();

1. Shallow cloningCopy the code

var obj = { name : ‘abc’, age : 123, sex : ‘female’ } var obj1 = {} function clone(origin,target){ for(var prop in origin){ target[prop] = origin[prop]; } } clone(obj,obj1); // Print obj1 to show that it has been copied

Implement fault tolerance:Copy the code

The original value is fine, but the reference value is copied:Copy the code

## 2. Deep clone two people, clone, only consider the array of reference values, object core: distinguish arrays and objectsCopy the code

Var obj = {name: ‘ABC ‘, age: 123, sex: ‘female’, card: [‘visa’,’unionpay’,[1,2]]} var obj1 = {card: [obj.card[0],obj.card[1],[]] } clone(obj, obj1);

Copy the code

var obj = { name : ‘abc’, age : 123, card : [‘visa’, ‘master’], wife : { name : “bcd”, son : { name : }} var obj1 = {name: obj. Name, age: 123, card: [] [obj.card[0],obj.card[1]], wife: {name: “BCD “, son: {name:” BCD “, son:}}

Object traversal for(var prop in obj) Traversal not only traversal objects, but also traversal groupsCopy the code

var arr = [‘a’,’b’,’c’] for(var prop in arr) { arr[prop] }

Typeof () : null typeof() : null typeof() : null There are three ways to use arrays or objects: Instanceof toString constructor is recommended because the other two have minor problems and do not encounter parent-child domains: [] instanceof Array -- >false should true 3. Create corresponding arrays and objectsCopy the code

/ / a recursive function deepClone (origin, target) {var target = target | | {}; / / fault-tolerant toStr = Object. The prototype. ToString, arrStr = “[Object Array]”. / / than}

Code implementationCopy the code

To optimize theCopy the code

Ternary operators simplify codeCopy the code

Var obect.create (); Var obect.create (); Var obect.create (); Var obect.create (); Var obect.create (); Array literals var arr = [];Copy the code

Var arr = [1, 2, 3, 5]; // Sparse array


2.new Array(length/content);

Copy the code

Var arr = new Array(1,2,3,4,5);

The difference betweenCopy the code

var arr = new Array(10); Var arr1 = [10]; Var arr = new Array(10.2); // The length is 10.2

Read and write arraysCopy the code

Arr [num] = XXX; arr[num] = XXX; // Can overflow write, lengthen array

In JS, arrays do not fail even if they do not have the 10th bit, because arrays are the common method for object-based arrays. 7 reverse, change the original array sort, push, pop, shift, unshift, > push to increase the last of the array encapsulated push ()Copy the code

Var arr = [1, 2, 3]; Array.prototype.push = function (){array.prototype.push = function (){array.prototype.push = function (){array.prototype.push = function (){array.prototype.push = function (){ i < arguments.length; i++) { this[this.length] = arguments[i]; } return this.length; }

> pop: cut out the last bit of the array arr.pop(); > shift: Reverse: reverse > sort arr.sort(); reverse: reverse > sort arr.sort(); Var arr = [1,2,10,2,4,5]; var arr = [1,2,10, 5]; Cannot implement the desired sort implement sort :(bubble sort) 1. Must have two parameters 2. Look at the return value (1) return a negative value, the first number before (2) is positive, the following number before (3) is 0, do not moveCopy the code

Var arr =,2,10,2,4,5 [1]; arr.sort(function (a, b) { if(a > b) { return 1; }else{ return -1; }});

Simplify the codeCopy the code

arr.sort(function (a, b) { if(a – b > 0) { return a – b; }else{ return a – b; }});

In the endCopy the code

arr.sort(function (a, b) { return a – b; //return b – a; / / descending});

Give an ordered array out of orderCopy the code

Math. The random () returns (0, 1) random number / / var arr =,2,3,4,5,6,7 [1]; // arr.sort(function () {// return math.random () -0.5; });

Object age sortCopy the code

String length sortCopy the code

var arr = [‘ac’,’bcd’,’cccc’,’asfsadshilk’,’casuicbniasbnciuas’]; arr.sort(function (a, b){ return a.length – b.length; })

Byte length sortCopy the code

> splice: sliceCopy the code

Arr.splice (1,2); // arr.splice(1,2); Var arr = [1,1,2,2,3,3]; Arr. Splice,1,0,0,0 (1); Var arr =,2,3,5 [1]; Arr. Splice (3,0,4); Arr. Splice (-1,1); // First to last

-1 is the last; How do I get the second to last of 1Copy the code

splice = function(pos) { pos += pos>0? 0:this.length; / / negative}

Join -- >split,toString > 0. Concat joinCopy the code

Var arr = [6]; Var arr1 =,8,9 [7]; arr.concat(arr1);

> toString turns arrays into strings > SliceCopy the code

Var arr = [6]; Var newArr = arr. Slice (1,3); var newArr = arr. Slice (1) var newArr = arr.slice(-4)//-4+6 bits // 3. No parameters: full interception

> join implements string joinCopy the code

Var arr = [1, 2, 3, 4]; Arr. Join (“-“)// The value must be a string of characters arr = [1-2-3-4];

Word-wrap: break-word! Important; "> < span style =" max-width: 100%Copy the code

var arr = [1-2-3-4]; Arr.split (“3”)// Must be a string

We can use property names to emulate property 2 of arrays. 3. If you force the array to call push, the length property will be expanded according to the position of the length property value.Copy the code

function test() { console.log(arguments); arguments.push(7); } test(1,2,3,4,5,6);

The phenomenon ofCopy the code

/ / complete the basic form of an array of class build var obj = {” 0 “: ‘a’,” 1 “, “b”, “2” : “c”, “length” : 3, “push” : Array.prototype.push } obj.push(‘d’); // Results in length=4 and “3”:d

Class array: objects that can be used as arraysCopy the code

var obj = { “0” : ‘a’, “1” : ‘b’, “2” : ‘c’, “length” : 3, “push” : Array.prototype.push, “splice” : Array.prototype.splice// array.prototype.splice // array.prototype.splice // array.prototype.splice // array.prototype.splice // array.prototype.splice //

Length internal operation:Copy the code

Array.prototype.push = function(target) { this[this.length] = target; this.length ++; } // Array.prototype.push = function(target) {obj[obj.length] = target; obj.length ++; }

Class array to iterate over all the elementsCopy the code

var obj = { “0” : “a”, “1” : “b”, “2” : “c”, name : “abc”, age : 123, length : 3, push : Array.prototype.push, splice : Array.prototype.splice } for(var prop in obj){ console.log(obj[prop]) }

Type Typeof ([])-- Array Typeof ({})-- Object Typeof (function)-- function Typeof (new Number())-- new Object Typeof (123)-- number typeof(123)-- number typeof(123)-- numberCopy the code

Array de-duplication, programming hash hash on the prototype chainCopy the code

Var arr =,1,1,1,2,2,2,2,2,1,1,1,0,0 [1]; Array.prototype.unique = function() { var temp = {}, arr = [], len = this.length; For (var I = 0; i < len; i++){ if(! Temp [this[I]]) {temp[this[I]]; Temp [this[I]] = “ABC “; arr.push(this[i]); } } return arr; }

# Ternary operator form: judgment statement? If true, execute and return the result: If false, execute and return the result The trinary operator is a simplified version of if(){... }else{} Yes: No and returns a valueCopy the code

var num = 1 > 0 ? 2 + 2:1 + 1; var num = 1 > 0 ? “9” (” 10 “>? 1:0) : 2;

# try... Catch try{} Catch (e) {} Finally {}Copy the code

//try… catch try{ console.log(‘a’); console.log(b); console.log(‘c’); } catch(e) { } console.log(‘d’); // If an error occurs in a try, the code in the try will not be executed, and the AD will be printed

About the catchCopy the code

try{ console.log(‘a’); console.log(b); console.log(‘c’); }catch(e){//error error.message error.name —> error console.log(e.name + ” : ” + e.message);

} console.log(‘d’);

A small problemCopy the code

try{ console.log(‘a’); console.log(b); console.log(c); }catch(e){console.log(e.name + “:” + e.message);}catch(e){console.log(e.name + “:” + e.message); } console.log(‘d’);

The six values of error.name correspond to the following information: EvalError: the use of eval() is inconsistent with the definition.RangeError: a value is out of bounds.ReferenceError: an invalid or unrecognized value. TypeError: TypeError: operand TypeError; URIError: URI handler error; Es5.0 +**es5.0 +** ES5.0 +**es5.0 +**es5.0 +**es5.0 +**es5.0 +**es5.0 +**es5.0 Otherwise, ES3.0 "Use Strict" is no longer compatible with some irregular syntax of ES3. Use the new ES5 specification. Demo1: ES5 does not allow arguments.calleeCopy the code

Function test() {console.log(arguments.callee); function test() {console.log(arguments. } test();


demo2

Copy the code

function demo() { console.log(arguments.callee); } demo(); //es3.0 function test() {“use strict”// internal es5.0 console.log(arguments.callee); } test();

Two usages: Global strict mode A strict mode within a local function (recommended) is a string that does not affect browsers that do not support strict mode: With (){} with can change the scope chain, with(obj) obj as the top AOCopy the code

demoCopy the code

var obj = { name:”obj”, age:234 } var name = “window”; function test(){ var age = 123; var name = “scope”; with(obj){ console.log(name); //obj console.log(age); //234 } } test();

With simplifies codeCopy the code

var org = { dp1 : { jc : { name : ‘abc’, age : 123 }, deng : { name : “xiaodneg”, age : 234 } }, dp2 : {}} with(org.dp1.jc) {// Directly access console.log(name) in org.dp1.jc; }

Application: Document is also an objectCopy the code

document{ write : function () {} } with(document) { write(‘a’); }

Is not supported with the arguments. The callee, func. Caller, variable assignment must be declared before the local this must be the assignment, (Person) call (null/undefined) anything assignment), refused to repeat properties and parametersCopy the code

“use strict” function test(){ console.log(this); //undefined } test();

The newCopy the code

“use strict” function Test(){ console.log(this); } new Test();

Precompile In ES5 strict mode this does not point to window, it does not point to (null), this must be assigned, what is assignedCopy the code

“use strict” function Test(){ console.log(this); } Test.call({});

Assign a value of 123Copy the code

“use strict” function Test(){ console.log(this); } Test.call(123);

123 is the raw value :ES3 becomes the wrapper classCopy the code

function Test(){ console.log(this); } Test.call(123);

In strict mode, globally, this refers to the windowCopy the code

“use strict” console.log(this);

Es5 refuses to duplicate the ** attribute and parameter **. Duplicate attributes and arguments are not reported in ES3Copy the code

function test (name , name){ console.log(name); } / / test (1, 2); //test(2);

Parameter errorCopy the code

“use strict” function test (name , name){ console.log(name); } the test (1, 2);

Property does not report errorsCopy the code

Var obj={name:’112′, name:’111′} test(1,2);

Eval: 0.es3 cannot be eval(); Eval can execute stringsCopy the code

“use strict”; var a = 123; eval(‘console.log(a)’); // The string is executed in eval

Why not use with(); With can change the scope chain, change the scope chain, will reduce the efficiency The youth online < https://www.yuque.com/docs/share/7773dc1a-cd7d-4bf2-9b5a-170194ad9a56 > MDN website internal documentCopy the code

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Native JS objects wrap a chain of prototyped classes

object

1. Add, delete, modify and search attributes

2. Object creation method

A wrapper class

1. The little knowledge

2. The phenomenon:

prototype

Definition 1.

2. Extract common attributes.

3. Add, delete, change and check the original form

Prototype chain

1. Add, delete, modify and check the attributes on the prototype chain

2. About the toString:

3. The little bug

call/apply `Forbid to`

1.call

2. Apply:

Succession history

1. Traditional form

2. Borrow constructors

3. Share prototypes

4. Holy Grail mode

Through the prototype chain

Kind of yahoo!

The namespace

1. The old way: namespaces

2. New approach: Privatize variables with closures

Native JS objects wrap a chain of prototyped classes

object

1. Add, delete, modify and search attributes

2. Object creation method

A wrapper class

1. The little knowledge

2. The phenomenon:

prototype

Definition 1.

2. Extract common attributes.

3. Add, delete, change and check the original form

Prototype chain

1. Add, delete, modify and check the attributes on the prototype chain

2. About the toString:

3. The little bug

call/apply Forbid to

1.call

2. Apply:

Succession history

1. Traditional form

2. Borrow constructors

3. Share prototypes

4. Holy Grail mode

Through the prototype chain

Kind of yahoo!

The namespace

1. The old way: namespaces

2. New approach: Privatize variables with closures

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