Interview questions and answers (drawing analysis), have you been asked? Not much, but it can help you… (a)

Note: individual difficult to understand my drawing analysis, simple, easy to understand my text elaborated oh ~

console.log([]==false) console.log(! []==false) Copy code Copy codeCopy the code

Resolution:

2. Interview Questions:

let res = parseFloat('left:200px'); if(res===200){ alert(200); }else if(res===NaN){ alert(NaN); }else if(typeof res==='number'){ alert('number'); }else{} Copy code Copy codeCopy the code

Resolution:

Because NaN is a non-number, but it is of type Number, the result is’ Number ‘not Number

Why strings? Because alert and document output are strings

Interview question 3.

var a={}, b='0', c=0; a[b]='123'; a[c]='568'; console.log(a[b]); Copy code Copy codeCopy the code

Answer: 568

Interview question 4:

var a={}, b=Symbol('1'), c=Symbol('1'); a[b]='1'; a[c]='2'; console.log(a[b]); Copy code Copy codeCopy the code

Answer: 1.

The Symbol creates a unique value

Interview question 5:

var a={}, b={n:'1'}, c={m:'2'}; a[b]='11'; a[c]='2'; console.log(a[b]); var a = {n: 1}; var b = a; a.x = a = {n: 2}; console.log(a.x); console.log(b); Copy code Copy codeCopy the code

The answer:

2

undefined

{n: 1, x: {… }}

Resolution:

a[b]=’11’; =>a[object Object]=’11’

a[c]=’2′; =>a[object Object]=’2′

The latter overwrites the former, so console.log(a[b]); Is 2

Interview question 6:

let a=12; let b=13; function func(){ let a=1; let b=2; } console.log(a,b) Copy code Copy codeCopy the code

原 文 : Uncaught SyntaxError: Identifier ‘a’ has already been declared

Interview question 7:

function Func(x, y) { let total = x + y; this.result = total; this.say = function () {}; } let f1 = new Func(10, 20); console.log(f1); console.log(f1.total); console.log(f1.result); let f2 = new Func(); console.log(f2); Console. log('say' in f1) Copies code Copies codeCopy the code

The answer:

Func {result: 30, say: ƒ}

undefined

Func {result: NaN, say: ƒ}

true

Drawing helps you understand the principle:

Question 8 :(baidu second surface) implement the function fn, so that it has the following functions

Let res = fn (1, 2) (3); console.log(res); //=>6 1+2+3 Copy code Copy codeCopy the code

A. the b. the C. the D. the

function compose(... Funcs) {// funcs: Store sequentially executed functions (array) =>[fn1, fn3, fn2, fn4] return function anonymous(... >[20] if (funcs.length === 0) return args; // funcs.length === 0; if (funcs.length === 1) return funcs[0](... args); Return funcs.reduce((N, func) => {// The value of N for the first time: the argument func for the first function is the first function // the value of N for the second time: the value returned by the last func execution, As an argument to the next function: return array.isarray (N)? func(... N) : func(N); }, args); }; }let res = compose(fn1, fn3, fn2, fn4)(20, 30); //compose(fn1, fn3, fn2, fn4) is executed, and its return value is followed by (20,30)console.log(res); Copy code Copy codeCopy the code

Interview question 9: Implement function fn with the following functions

One of the most important concepts in functional programming is function composition, which is essentially connecting functions that process data like pipes, and then passing the data through the pipes to get the final result. For example, const add1 = (x) => x + 1; const mul3 = (x) => x * 3; const div2 = (x) => x / 2; div2(mul3(add1(add1(0)))); //=>3 For compose, we can construct a compose function that takes any number of functions as arguments (each of which takes a single argument), and then compose returns a function that does the following:  const operate = compose(div2, mul3, add1, Div2 (mul3(add1(add1(0)))))) //=> div2(mul3(add1(add1(2))))) Compose (f, g, h)(x) : compose(f, g, h)(x) for composeCopy the code

Answer:

*/ const fn1 = (x, y) => x + y + 10; /* * compose: const fn1 = (x, y) => x + y + 10; const fn2 = (x) => x - 10; const fn3 = (x) => x * 10; const fn4 = (x) => x / 10; // let res = fn4(fn2(fn3(fn1(20)))); // console.log(res); function compose(... Funcs) {// funcs: Store sequentially executed functions (array) =>[fn1, fn3, fn2, fn4] return function anonymous(... >[20] if (funcs.length === 0) return args; // funcs.length === 0; if (funcs.length === 1) return funcs[0](... args); Return funcs.reduce((N, func) => {// The value of N for the first time: the argument func for the first function is the first function // the value of N for the second time: the value returned by the last func execution, As an argument to the next function: return array.isarray (N)? func(... N) : func(N); }, args); }; } let res = compose(fn1, fn3, fn2, fn4)(20, 30); //compose(fn1, fn3, fn2, fn4) is executed, and its return value is followed by (20,30) console.log(res); Copy code Copy codeCopy the code