Array declaration and reading and writing

  1. Array literal declaration

    var arr = [1.2.3.4];
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  2. Constructor declaration

    var arr = new Array(1.2.3);
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  3. Type conversion declaration

    var arr = Array(1.2.3);
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    All arrays inherit from Array.prototype

    If the constructor is given a single argument num, it declares an array of num length empty, i.e. undefined

  4. Poor array

    var arr = [, 2.4,];
console.log(arr);
// empty, 2, empty, 4
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    Array literals can be defined as sparse arrays, printing empty where no value is given, which is actually undefined. Note that the last “, “does not count

  5. Arrays are based on key-value pairs of objects

    var arr = [1.2.3.4.5];
var obj = {
	0: 1.1: 2.2: 3.3: 4
};
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    Array overrides the toString method of Object

  6. Reading and writing arrays

    Use the subscript (index) to read the data in the corresponding position, and return undefined if there is none

    var arr = [, 2.4,];
arr[0] = 1;
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Push () and the unshift ()

The push and unshift methods inherit from Array.prototype

Push adds one bit after the last bit of the array, and unshift adds one bit before the first

The parameter is the content to be added, which can be multiple

Returns the added length of the array

var arr = [1.2.3];
arr.push(4.5);
arr.unshift(0);
console.log(arr);
// [0, 1, 2, 3, 4, 5]
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Pop (), and the shift ()

The pop and shift methods inherit from Array.prototype

Pop deletes the end of the array, shift deletes the first

Returns the deleted value

var arr = [1.2.3];
console.log(arr.pop());
console.log(arr);
console.log(arr.shift());
console.log(arr);
/ / 3
/ / 1. 2
/ / 1
/ / 2
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reverse()

The reverse method inherits from Array.prototype

Inverts the contents of the array and returns the inverted array

var arr = [1.2.3];console.log(arr.reverse());/ / [3, 2, 1)
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splice()

The splice method inherits from Array.prototype

Clipping the contents of the array, you can clipping places to add data that will affect the original array

Parameters: start subscript, cut length, data added at start subscript position

Returns the clipped subarray

var arr = [1.2.3];console.log(arr.splice(1));console.log(arr);/ / / / [1] [2, 3]
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For the first parameter only, cut all data from the beginning subscript to the end

If it’s negative, it starts at -1 and goes backwards

var arr = [1.2.3];console.log(arr.splice(1.1));console.log(arr);/ / [2] / [1, 3]
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Give two parameters, representing the start subscript and the shear length

var arr = [1.2.3];console.log(arr.splice(1.1.100.101));console.log(arr);// [1, 100,101, 3]
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For the three parameters, cut and add data after the start subscript position

slice()

Like splice(), copies the contents of an array and returns it, but does not affect the original array

Parameters: start subscript, end subscript, excluding end subscript, left closed right open

var arr = [1.2.3];console.log(arr.slice(0.2));console.log(arr);// [1, 2]// [2, 3]
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sort()

The sort method is used to sort arrays, inherited from array.prototype

The default is to sort by ASCII

Change the contents of the array and return the sorted array

```javascriptvar arr = [1, 4, 2, 3, 30]; console.log(arr.sort()); // [1, 2, 3, 30, 4]Copy the code

The sort method gives a function(a, b){} that ranks a after B if it returns a positive number; otherwise, a precedes b

var arr = [1.3.14.27.5.4];console.log(arr.sort(function(a, b) {	returna - b; }));// [1, 3, 4, 5, 14, 27]
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Math.random() returns a random number between (0, 1) and sort the array because math.random () -0.5 returns a random number between (-0.5, 0.5)

var arr = [1.2.3.4.5.6];console.log(arr.sort(function(a, b) {	return Math.random() - 0.5; }));Copy the code

concat()

Used to concatenate two arrays and return the concatenated array as the array to be concatenated later

var arr1 = [1.2.3];var arr2 = [4.5.6];console.log(arr1.concat(arr2));// [1, 2, 3, 4, 5, 6]
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toSting()

Converts an array to a string and returns the string, separated by commas

var arr = [1.2.3];console.log(arr.toString());
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Jion (), and the split ()

  1. The jion method converts an array to a string and returns the string with the argument as a delimiter

  2. The split() method converts a string into an array and returns the first argument of the array as a delimiter, the second argument as the first bits, or none at all

    var arr = [1.2.3]; str = arr.join(The '-');console.log(str);console.log(str.split(The '-'));console.log(str.split(The '-'.2));[1, 2] // [1, 2]
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filter()

Compatible with Internet Explorer 9 or later

Used to filter the contents of an array. The return value of the parameter method determines whether the corresponding element is left or not. If false is returned, the element is discarded

Var arr = [0, 1, 2, 2, 3, 4, 4, 0, 1]; Funtion uniqe(arr) {return arr. Filter (function(item, index, arr) { Return arr.indexof (item) === index; }); }// Method defect: cannot remove [{}, {}]
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An array of class

  1. Class arrays are similar to arrays such as Arguments, NodeList, etc. They have length attributes and even forEach attributes

  2. Class arrays don’t inherit array. prototype. They don’t have push, splice, etc

  3. Both the class array and the underlying array are object-based key-value pairs

  4. Class arrays that do not support Array methods can be operated on by borrowing array.prototype

    var obj = {    2: 3.3: 4.length: 2.push: Array.prototype.push}obj.push(1); obj.push(2);console.log(obj);// {// 2: 1,// 3: 2,// length: 4,// push: push(){}// __poroto__: {... } / /}
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    Array.prototype.push (); array.prototype (); array.push ()

    Array.prototype.push = function (elem) {    this[this.length++] = elem; }Copy the code