Detailed explanation of js deletion operation delete steps

Introduction

Used to delete the attributes of an object.

Grammar

delete expresson

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express should be a reference to an object, such as

delete object.propertydelete object['property']

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If expression is not a reference to an object, delete will have no effect

Return value

In strict mode, if the attribute is a non-configurable attribute, an exception will be thrown when deleted. In non-strict mode, false is returned, and in other cases, true is returned. .

Function

1. You can delete implicit global variables, but you cannot delete explicit global variables.

   Global variables are actually properties of the global object (window).
   

x = 10;var y = 20;delete x; //true;delete y; //false

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The built-in properties of built-in objects cannot be deleted, but user-defined properties can be deleted.

1. obj = {
   
       h : 10}var obj1 = {
       h: 10}delete Math.PI; // falsedelte obj.h; //truedelete obj; //ture ,obj 是全局变量的属性，而不是变量。delete obj1.h;//truedelete obj1; //false 全局显示变量不能被删除function fn(){
   
       var z = 10;    delete z; //false
       //z是局部变量，不能被删除，delete只能删除对象的属性。}delete fn; //false//fn 相当于是一个匿名变量，所以也不能被删除。

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• Cannot delete an object from Properties inherited from the prototype, but you can delete it directly from the prototype;

function foo(){}
foo.prototype.name = 'zhangsan';var f = new foo();//delete只能删除自己的属性，不能删除继承来的属性delete f.name; // false console.log(f.name);//zhangsandelete foo.prototype.anme; // trueconsole.log(f.name); // undefined

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• Delete array elements

• When you delete array elements, the length of the array does not become smaller.

  var arr = [1,3,4,6,73,2];delete arr[2];
  
  console.log(arr.length); // 6console.log(arr[2]); //undefiendconsoel.log(arr); //[ 1, 3, , 6, 73, 2 ]

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• Function: Deleting elements in the forEach loop will not affect the loop result

var arr = [1,3,5,21,3,4,53,21,5,2];

arr.forEach(function(val,index){

    if(val < 10){        delete arr[index];
    }
})

console.log(arr); //[ , , , 21, , , 53, 21, ,  ]//可以使用filter过滤掉空值 [ 21, 53, 21 ]arr = arr.filter(function(val){return val});

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• Compare with Array.splice

• arr.forEach(function(val,index){
  
      if(val < 10){
  
          arr.splice(index,1);
      }
  })//没有答案我们预想的结果，因为splice删除元素会改变数组的长度。//所以说删除一个值后，其后的那个值占据了它的位置，在判断的时候就会漏掉。console.log(arr);// [ 3, 21, 4, 53, 21, 2 ]

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•         <link rel="stylesheet" href="https://csdnimg.cn/release/phoenix/template/css/markdown_views-ea0013b516.css">
              </p>

  Related recommendations ：

• Using Js to implement several methods of deleting one or more items in an array

• Introduction to methods of deleting specific elements in JavaScript arrays

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