How to delete an array element in es6

Method: 1. Use shift() to delete the first element, the syntax is "array.shift()"; 2. Use pop() to delete the last element, the syntax is "array.pop()"; 3 , use length to delete the last element, the syntax is "array.length=original array length - 1"; 4. Use delete to delete an element with a specified subscript, the syntax is "delete array name [subscript]"; 5. Use splice() to delete An element at any position, the syntax is "array.splice(position,1)".

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

Method 1: Use the shift() function to delete the first array element

array.shift() function can convert the array The first element is removed from it and the value of the first element is returned; then all remaining elements are shifted forward by 1 position to fill the gap at the head of the array.

var a = [1,2,3,4,5,6,7,8];  //定义数组
a.shift();
console.log(a);

The output result is:

Note: The shift() method will change the original array and modify the length of the array!

Method 2: Use pop() to delete the last array element

array.pop() method can delete the last element in the array , and returns the deleted element.

var a = [1,2,3,4,5,6,7,8];  //定义数组
a.pop();
console.log(a)

The output result is:

Note: The pop() method will also change the original array and modify the length of the array!

Method 3: Use the length attribute to delete the last array element

The length attribute of the array is generally used to set or return the elements in the array Number, that is, setting or returning the array length.

We can use the feature of setting the length of the array and set the length attribute to be smaller than the original length to delete one or more elements from the end of the array; if the value is set to 0, the entire array will be deleted. That is, clear the array!

Syntax:Array object.length=original array length-1;

Example:

var a = [1,2,3,4,5,6,7,8];  //定义数组
console.log(a)
a.length=7;
console.log(a)

Method 4: Use the delete operator to delete an element at the specified subscript

We all know that each element in the array has a serial number, and this serial number starts from Starting from 0, it is called the index. According to this array subscript, we can use the form array name[subscript] to access the element of the specified subscript.

After accessing the specified element, you can use the delete operator to delete the element, but the length of the array will not change; the deleted element will change It is a gap element.

var arr=new Array("香蕉","苹果","梨子","橙子","橘子","榴莲");
console.log(arr);

delete arr[1];  //删除下标为1的元素（第二个元素）
console.log(arr);

The gap element can be read and written. The length attribute does not exclude gaps. The return value of the null element position is undefined

console.log(arr[1]);

Explanation: An empty element and an element whose value is undefined are two different concepts. Even the return value of an empty element is undefined. When JavaScript initializes an array, it can allocate memory only if it actually stores valuable elements.

Method 5: Use splice() to delete an element at any position

Use splice() to delete an element from the specified subscript position Start deleting one or more elements.

Syntax for deleting elements:

array.splice(index,howmany)

• The first parameter index can specify the starting subscript position (that is, the position where the element is deleted) ;

• The second parameter howmany specifies the number of elements that should be deleted (that is, one or more elements that need to be deleted).
  

You only need to set the second parameter howmany to 1, that is, delete an element at any index position.

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

var arr= [1,2,3,4,5];
console.log(arr);

arr.splice(1,1);
console.log(arr);

Using the splice() method, we can also delete elements at the beginning and end of the array. ：

• If you want to delete elements at the beginning of the array, just set the value of the first parameter index of this method to 0

var arr= [1,2,3,4,5];
console.log(arr);

arr.splice(0,1);
console.log(arr);

• If you want to delete an element at the end of the array, set the value of the first parameter index of this method to a negative number, then the absolute value will be calculated from the right side of the array to the Positioning on the left; and the value of the second parameter howmany must be equal to the value of index.

var arr= [1,2,3,4,5];
console.log(arr);

//从倒数第1个元素开始，截取1个元素
arr.splice(-1,1);
console.log(arr);

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