JS array learning: adding elements based on array subscripts

In the previous article "How to insert elements at the head or tail of JS array learning?》, we introduced three ways to add elements at the beginning or end of an array. This time we continue to learn about the method of adding array elements and introduce how to add elements according to the array subscript. Interested friends can learn about it~

Each element in the array has a serial number. This The serial number starts from 0 and is called the index. The subscript of the array is very important. We can use the subscript to access the array elements. We only need to specify the subscript, in the form:array name[subscript index]. Example:

a[0] //表示第0个元素 a[3] //表示第3个元素

We can also insert elements using subscripts. Let’s introduce them in detail below.

We can use the formarray name[subscript value] = element valueto add a new element at the specified subscript position of the array

var a = [1,2,3]; //定义数组 a[3] = 4; //为数组添加一个元素 console.log(a); //返回[1,2,3,4]

Look at the output result:

However, when using this method, you need to specify the subscript value >= the length of the original array, so that a new element will be added to the end of the original array

var a = [1,2,3]; //定义数组 a[4] = 4; //为数组添加一个元素 console.log(a);

Look at the output result:

var a = [1,2,3]; //定义数组 a[1] = 4; //为数组添加一个元素 console.log(a);

Array name [subscript value] = element valuecan only be used in the array Add a new element at the specified subscript position; so what do you do if you want to insert one or more elements at the specified subscript position?

We can use the splice() method.splice() is a powerful method that can not only delete array elements, but also add array elements and replace array elements.

array.splice(index,howmany,item1,...,itemX)The first parameterindexspecifies the starting subscript position; The second parameterhowmanyspecifies 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 subsequent parametersitem1,... ..,itemXto insert one or more elements.

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

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);

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:

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

array length. The array length can be obtained usinga.length.

var a = [1,2,3,4,5]; a.splice(5,0,[6,7,8,9]); console.log(a);

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