How to add elements to an array in javascript

Methods to add elements: 1. Use the unshift() function to insert elements at the beginning of the array; 2. Use the push() function to insert elements at the end of the array; 3. Use the concat() function to insert elements at the end of the array; 4. Use the splice() function to add elements at any position based on the array subscript.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

javascript adds elements to the array

Method 1: Use the unshift() function

Use the unshift() function to insert elements at the beginning of the array. This function can append one or more parameter values ​​to the head of the array:

array.unshift(元素1, 元素2, ..., 元素X)

1st parameter Element 1 is the new element 0 of the array, the second parameter element 2 is the new element 1, and so on, and finally returns the length of the array after adding the element.

Let’s take a closer look at the following example:

var a = [0];  //定义数组
console.log(a);  //返回[0]

a.unshift(1,2);  //一次性增加两个元素
console.log(a);  //返回[1,2,0]

var a = [0];
a.unshift(1);  //增加元素1
a.unshift(2);  //增加元素2
console.log(a);  //返回[2,1,0]

It can be seen that we use a.unshift(1,2) to press at the beginning of the a array Insert two values ​​​​1 and 2 sequentially; use a.unshift(1) to insert the value 1 at the beginning of the a array, and then use a.unshift(2) at the beginning (that is, before the value 1 ) insert the value 2. Therefore, the output result is:

Method 2: Use the push() function

The push() method can push one or more The parameter value is appended to the end of the array and the length of the array after adding elements is returned.

array.push(元素1, 元素2, ..., 元素X)

Let’s take a closer look at the following example:

var a = [0];  //定义数组
console.log(a);  //返回[0]

a.push(1,2);  //一次性增加两个元素
console.log(a);  //返回[0,1,2]

var a = [0];
a.push(1);  //增加元素1
a.push(2);  //增加元素2
console.log(a);  //返回0,1,2]

It can be seen that we use a.push(1,2) to press at the end of the a array Insert two values ​​​​1 and 2 sequentially; use a.push(1) to insert the value 1 at the end of the a array, and then use a.push(2) on this basis. Insert a value 2 at the end (that is, after the value 1). Therefore, the output result is:

Method 3. Use the concat() function

In addition to inserting elements at the end of the array, you can use push( ) function, you can also use the concat() function.

The concat() method can also insert a given element or elements, and can add all parameters passed to the end of the array in order.

var a = [1,2,3,4,5];  //定义数组
var b = a.concat(6,7,8);  //为数组a连接3个元素
console.log(b);  //返回[1,2,3,4,5,6,7,8]

The output result is:

Explanation: The concat() method will create and return a new array instead of based on the original one Add new elements.

Method 4: Use the splice() function

How to insert one or more elements at a specified subscript position?

The answer is: You can use the splice() method.

array.splice(index,howmany,item1,...,itemX)The first parameter index is the specified starting point mark position; the second parameter howmany specifies the number of elements that should be deleted. When the value is set to 0, the deletion operation will not be performed; in this way, the third and following parameters item1, .....,itemX to insert one or more elements.

Let’s take a closer look at the following example:

var a = [1,2,3,4,5];
a.splice(1,0,"hello");
console.log(a);

It can be seen that: use a.splice(1,0,"hello") in the subscript 1 Insert an element "hello" at the position (that is, after the first element position of the array), so the output result is:

var a = [1,2,3,4,5];
a.splice(2,0,"hello","hi",8);
console.log(a);

You can see Exit: Use a.splice(2,0,"hello","hi",8)Insert multiple elements at the position of subscript 2 (that is, after the second element position of the array)" hello", "hi", 8, so the output result is:

Using the splice() method also You can add elements at the beginning or end of the array:

var a = [1,2,3,4,5];
a.splice(0,0,"hello");
a.splice(a.length,0,"hi");
console.log(a);

If you want to add an element at the beginning of the array, just set the value of the first parameter index of this method to 0; if you want to add an element at the end of the array , just set the value of the first parameter index of the method to array length. The array length can be obtained using a.length.

Let’s take a look at the output:

[Recommended learning: javascript advanced tutorial]

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