Important features of ES5

Version awareness

• ECMA Script (developed by the ECMA organization) is the specification, and JavaScript is the implementation.
• ES5 （2009） 、 ES6 （2015） 、 ES7 （2016）
• IE browser has some support problems for ES5.

1. Strict mode ('use strict'): Make Javascript run under stricter grammatical conditions

• Variable: declaration must use var
• Object: attributes cannot be repeated
• Function: The custom function this cannot point to the window object, add scope to the eval function

2. json: The syntax for storing and exchanging text information

• json.stringFy(): javascript object/array to json text.
• json.parse(): Convert json text to javascript object/array.

Three. Object extension

• 1.Object.create(prototype, [descriptors]): Create a new object with the specified object as the prototype

  var obj = {
    
    firstName:"张",lastName:'三'};
  var newObj = null;
  // 一：ES5构建对象：Object.create
  newObj = Object.create(obj,{
    
    
    sex:{
    
    
      value:"男",
      writable:true,// 可修改
      configurable:true,// 可删除
      enumerable:true // 可枚举
    }
  });

• 2.Object.defineProperties(object, descriptors): extend multiple properties for the specified object

var strongObj = {
    
    
    firstName:"张",
    lastName:'三',
    get fullName(){
    
    
      return this.firstName+this.lastName;
    },
    set fullName(name){
    
    
      var arr = name.split("");
      this.firstName = arr[0];
      this.lastName = arr[1];
    }
  };
  
  var obj = {
    
    firstName:"张",lastName:'三'};
  var strongObj1 = {
    
    firstName:"张",lastName:'三'};
  // 二：ES5增强对象：Object.defineProperties（添加存取器/计算属性）
  Object.defineProperties(strongObj1,{
    
    
    fullName:{
    
    
      get:function(){
    
    
        return this.firstName+this.lastName;
      },
      set:function(name){
    
    
        var arr = name.split("");
        this.firstName = arr[0];
        this.lastName = arr[1];
      }
    }
  });

Four. Array extension

• 索引：Array.prototype.indexOf/ lastIndexOf (value)
• 遍历：Array.prototype.forEach(function(item, index){})
• 映射：Array.prototype.map(function(item, index){})
• 过滤：Array.prototype.filter(function(item, index){})

  var arr = [6,2,4,6,1,6];
  console.log(arr.indexOf(6),arr.lastIndexOf(6));
  arr.forEach(function(item){console.log(item)});
  console.log(arr.map(function(item){return item+10}));
  console.log(arr.filter(function(item){return item>4}));

Five. Function extension

• Function.prototype.bind(obj): bind this in the function to obj, and return the function
• Distinguish between bind, call and apply: distinguish from whether to execute immediately or pass parameters

function fn(param){
  console.log(this,param);
}
  var obj = {name:"张三"};
  fn("param");
  fn.call(obj,"call_param");
  fn.apply(obj,["apply_param"]);
  fn.bind(obj,"bind_param")();//不会立即执行，常用在回调函数。