How to remove elements from es6 array

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 splice() to delete elements at any position, the syntax is "array.splice(position, number)"; 4. Use length to delete the N elements at the end, the syntax is "array.length=original array length-N"; 5. Directly assign the empty array "[]" to clear the elements; 6. Use delete to delete an element at the specified subscript.

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 remove the first element of the array elements are 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 splice() to delete an element at any position

Use splice() to delete an or element starting from the specified subscript position Multiple 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);

Method 4: Use the length property to delete array elements (or even clear elements)

The length attribute of an array is generally used to set or return the number of elements in the array, that is, to set or return the length of the array.

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 1:

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

Example 2:

var a = [1,2,3,4,5,6,7,8];  //定义数组
console.log(a)
a.length=0;
console.log(a)

Method 5: Directly assign the empty array[]

Assigning it directly to an empty array[] will clear all previous elements.

var arr=new Array(1,2,3,4,5,6,7,8,9,10);
console.log(arr);
arr=[];
console.log(arr);

This method does not strictly clear the array, it just reassigns arr to an empty array.

Method 6: 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 , this serial number starts from 0 and 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.

访问到指定元素后，就可以利用 delete运算符 来删除该元素，但数组长度不会发生改变；删除后的该元素会变为空位元素，

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);

空位元素可以读写，length 属性不排斥空位，空元素位返回值为 undefined

console.log(arr[1]);

说明：空元素与元素的值为 undefined 是两个不同的概念，即使空元素的返回值也是 undefined。JavaScript 在初始化数组时，只有真正存储有值得元素才可以分配内存。

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