Introduction to commonly used methods of Array objects in JavaScript (code examples)

This article brings you an introduction to the commonly used methods of Array objects in JavaScript (code examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

In js, array is a special object. It is our commonly used data format. Today, let’s sort out the commonly used array methods.

1. Basics

A few basic ones will be briefly introduced:
Creating an array

var arr1 = new Array();  //括号可以传参，指定数组长度。目前arr1.length是0
var arr2 = new Array(3);//arr2.length是3
var arr3 = new Array(1,2,3,4);  //当传多个参数时，js会把这些参数作为数组的初始值。
console.log(arr3);  // [1,2,3,4]

new Array() There is one caveat when creating an array. When only one parameter is passed, if the value is non-numeric. will be used as the first parameter of the array, generating an array of length 1. If it is a number, an empty array of that number's length will be created.

But in fact, the above creation method is not commonly used. We are more accustomed to writing like this

var arr = [];
var arr = [0,1,2,3]

Basic method

arr.length  //数组的长度
arr[1] //数组下标是1的值。数组的下标从0开始计数
arr.push(值) //往数组添加元素

2. Other methods

var arr = ["element1","element2","element3","element4"];     //下面所有案列都是用的这个数组

//获取指定元素的下标
var index = arr. indexOf(”element2“）;   // 1

(1)splice(index,number,item1,...,itemX ) adds/removes elements from an array and returns the removed element.

##indexRequired. integer. The position at which items are added/removed, use negative numbers to specify the position from the end of the array. numberRequired. The number of items to delete. If set to 0, items will not be deleted. item1, ..., itemXOptional. New items added to the array.

Parameters	Description

Let’s look at the actual example

//删除
let getReturn = arr.splice(1,1);
console.log(getReturn);  // ["element2"]
console.log(arr);    //["element1",","element3","element4"]

//添加
let getReturn = arr.splice(arr.length,0,"element5","element6");
console.log(getReturn);  //[]
console.log(arr);    //["element1","element2","element3","element4","element5","element6"]

(2) pop() method, delete the last bit of the array and return the deleted element.

let getReturn = arr.pop();
console.log(getReturn);    //element4
console.log(arr);    //["element1","element2","element3"]

(3) slice(start,end) returns the selected element from the existing array.

Parameters Description ##startendNote: Please note that this method does not modify the array, but returns a subarray. If you want to delete a segment of elements from an array, you should use the method Array.splice().

Required. integer. The position at which items are added/removed, use negative numbers to specify the position from the end of the array.
Required. The number of items to delete. If set to 0, items will not be deleted.

let getReturn = arr.slice(1,3);
console.log(getReturn);    //["element2", "element3"]
console.log(arr);    //["element1", "element2", "element3", "element4"]

(4) join(separator) puts all elements in the array into a string.

separator: optional. Specify the delimiter to use. If this parameter is omitted, a comma is used as the delimiter.

let getReturn = arr.join();
console.log(getReturn);    //element1,element2,element3,element4
console.log(arr);    //["element1", "element2", "element3", "element4"]

(5) concat(array1,array2,...,arrayX) method is used to connect two or more arrays.

arrayX: required. This parameter can be a specific value or an array object. Can be any number.

//传数组
let getReturn = arr.concat(['element5',"element6"],["element7"]);
console.log(getReturn);    //["element1", "element2", "element3", "element4", "element5", "element6", "element7"]
console.log(arr);    // ["element1", "element2", "element3", "element4"]

//传元素
let getReturn = arr.concat('element5',"element6");
console.log(getReturn);    //["element1", "element2", "element3", "element4", "element5", "element6"]
console.log(arr);    //["element1", "element2", "element3", "element4"]

(6) The sort(sortby) method is used to sort the elements of the array.

sortby: Optional. Specifies the sort order. Must be a function.

Return value: reference to the array. Please note that the array is sorted on the original array and no new array is generated.

Comparison rules: Sort according to character encoding, so the result may not be the result you want, you have to pass parameters to solve it

let newArr = [3,5,2,4,1];

let getReturn = newArr.sort();
console.log(getReturn);      //[1, 2, 3, 4, 5]
console.log(newArr);    //[1, 2, 3, 4, 5]

Let’s look at another example that is not as good as we want

let newArr = [1000,88,93,6,34];
let getReturn = newArr.sort();
console.log(getReturn);    //[1000, 34, 6, 88, 93]
console.log(newArr);    // [1000, 34, 6, 88, 93]

//要实现大小排序，我们需要传参数解决
function sortNumber(a,b){    //定义函数
    return a - b
}
let getReturn = newArr.sort();
console.log(getReturn);    //[6, 34, 88, 93, 1000]
console.log(newArr);    //[6, 34, 88, 93, 1000]

(7) The shift() method is used to delete the first element of the array and return the value of the first element.

If the array is empty, the shift() method will do nothing and return an undefined value.

  let getReturn = arr.shift();
  console.log(getReturn);    //element1
  console.log(arr);    //["element2","element3","element4"]

(8) The unshift() method adds one or more elements to the beginning of the array and returns the new length.

arr.unshift(newelement1,newelement2,....,newelementX)

  let getReturn = arr.unshift("element-1","element0");
  console.log(getReturn);    //6
  console.log(arr);    //["element-1","element0","element1","element2","element3","element4"]

(9) The toString() method can convert the array into a string and return the result.

arr.unshift(newelement1,newelement2,....,newelementX)

  let getReturn = arr.toString();
  console.log(getReturn,typeof getReturn);    //element1,element2,element3,element4 string
  console.log(arr,typeof arr);    //["element1", "element2", "element3", "element4"] "object"

Note: When used for string operations, JavaScript will call this method to automatically convert the array into a string . For example:

let string = arr+"123";
console.log(string);    //element1,element2,element3,element4123

(10) The reverse() method is used to reverse the order of elements in the array.

This method will change the original array without creating a new array.

  let getReturn = arr.reverse();
  console.log(getReturn);    //["element4", "element3", "element2", "element1"]
  console.log(arr);    //["element4", "element3", "element2", "element1"]

3. Also

In addition, there are valueOf(), toLocaleString(), and toSource() methods. But I have never used it, and I don’t think of any usage scenarios, so I won’t talk about it separately.

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