Js array basic method summary

• instanceof

  console.log(a instanceof Array); // trueCopy the code

Only one global scope is used in this way. If the web page contains more than one frame, error prone.

• Array.isArray()

console.log(Array.isArray(a)); // trueCopy the code

It works regardless of how many global environments you have, but compatibility is not high.

• Object.prototype.toString.call()

console.log(Object.prototype.toString.call(a)); // [object Array]Copy the code

Use the toString function of the object to determine compatibility. Cannot use the array’s own toString because the function has been overridden.

• toLocaleString

  console.log(a.toLocaleString()); //a,b,cCopy the code

• toString

  console.log(a.toString()); //a,b,cCopy the code

• valueOf

  console.log(a.valueOf()); // Return itself ["a", "b", "c"]Copy the code

• join

  console.log(a.join('&')); //a&b&cCopy the code

Since the first two methods become strings with “, “in the middle by default, you can change the spacer using the join method.

• Extended operators (new in ES6)
  
  The extension operator is three dots (…) . It is like the inverse of the REST argument, turning an array into a comma-separated sequence of arguments.

  console.log(... [1, 2, 3)); // 1 2 3 console.log(1, ... [2, 3, 4, 5); // 1 2 3 4 5 [...document.querySelectorAll('div')]; // [<div>, <div>, <div>]Copy the code

• shift

Remove from head

console.log(a.shift()); // return the removed item aCopy the code

• Unshift is added from the header

console.log(a.unshift('a')); // Return the length of the arrayCopy the code

• Concat Concat in-depth parsing

• Slice Slice in-depth parsing

• splice

Always return the deleted item, or an empty array if none is present. The first parameter indicates the starting position; The second parameter indicates the number of deletions to be made (0, no deletions). The third parameter indicates the optional item to add;

var colors1 = ["red", "green", "blue"]; The console. The log (colors1. Splice (0, 1)); //["red"] console.log(colors1); / / / "green", "blue". The console log (colors1. Splice (0, 0, "aaa")); //[] console.log(colors1); / / / "aaa", "green", "blue"] the console. The log (colors1. Splice (0, 2, "SSS")); //["aaa", "green"] console.log(colors1); //["sss", "blue"]Copy the code

• CopyWithin () (new in ES6) Within the current array, copies the member in the specified location to another location (overwriting the original member), and returns the current array.

  Parameter list: -target (required) : Replace data from this position. - start (Optional) : reads data from this position. The default value is 0. If it is negative, it is the reciprocal. - end (Optional) : stops reading data before this position. The default value is the array length. If it is negative, it is the reciprocal.Copy the code

[1, 2, 3, 4, 5].copyWithin(0, 3); / / [4, 5, 3, 4, 5] / / copies the 3 to 0 bit [1, 2, 3, 4, 5]. CopyWithin (0, 3, 4); / / [4, 2, 3, 4, 5] / / - equivalent to the 3, 2-1 is equal to 4 [1, 2, 3, 4, 5]. CopyWithin (0, 2, 1); // [4, 2, 3, 4, 5]Copy the code

• Fill () (new in ES6) fills an array with the given value. The first parameter indicates the value of the fill, the second parameter indicates the start of the fill, and the third parameter indicates the one before the end of the fill.

['a', 'b', 'c'].fill(7); // [7, 7, 7] new Array(3).fill(7); // [7, 7, 7] ['a', 'b', 'c'].fill(7, 1, 2); // ['a', 7, 'c']Copy the code

They both return a traverser object, which can be used for… The of loop is traversed, the only differences being that keys() is traversal of key names, values() is traversal of key values, and entries() is traversal of key value pairs.

• entries()
• keys()
• values()

for (let index of ['a', 'b'].keys()) {
  console.log(index);
}
// 0
// 1
for (let elem of ['a', 'b'].values()) {
  console.log(elem);
}
// 'a'
// 'b'
for (let [index, elem] of ['a', 'b'].entries()) {
  console.log(index, elem);
}
// 0 "a"
// 1 "b"Copy the code

You can also call the next() method manually.

let letter = ['a', 'b', 'c'];
let entries = letter.entries();
console.log(entries.next().value); // [0, 'a']
console.log(entries.next().value); // [1, 'b']
console.log(entries.next().value); // [2, 'c']Copy the code