Javascript ES6中Object.key、Object.values、Object.entries

一、Object.keys

Object.keys() 方法会返回一个由一个给定对象的自身可枚举属性组成的数组，数组中属性名的排列顺序和正常循环遍历该对象时返回的顺序一致 。 

    let arr = ['a','b','c']
    console.log(Object.keys(arr))   //console：['0','1','2']

    let obj = {0:'a',1:'b',2:'c'}
    console.log(Object.keys(obj))  //console:['0','1','2']

    let objeAn = {100:'a',34:'b',23:'c'}
    console.log(Object.keys(objeAn)) //console:['23','34','100']

二、Object.values

Object.values()方法返回一个给定对象自身的所有可枚举属性值的数组，值的顺序与使用for...in循环的顺序相同 ( 区别在于 for-in 循环枚举原型链中的属性 )

    let obj = {item:'bar',unt:23}
    console.log(Object.values(obj))  //['bar','23']

    let obj1 = {0:'a',1:'b',2:'c'}
    console.log(Object.values(obj1)) // ['a','b','c']

    // getFoo不可枚举的属性
    let myobj = Object.create({},{getFoo:function () {return this.foo}})
    myobj.foo = 'bar'
    console.log(Object.values(myobj)) //['bar]
    
    //非对象参数强制为对象
    console.log(Object.values('att')) //['a','t','t']

三、Object.entries 

Object.entries()方法返回一个给定对象自身可枚举属性的键值对数组，其排列与使用 for...in 循环遍历该对象时返回的顺序一致（区别在于 for-in 循环还会枚举原型链中的属性）。

  let obj = { foo:'bar',baz:42 }
  console.log(Object.entries(obj))  //[ ['foo','bar'],['baz',42] ]

  let obj1 = {0:'a',1:'b',2:'c'}
  console.log(Object.entries(obj1)) //[ ['0','a'],['1','b'],['2','c'] ]

  let anObj = {100:'a',2:'b',7:'c'}
  console.log(Object.entries(anObj)) // [ ['2',''],['7','c'],['100','c'] ]

  let myObj = Object.create({},{getFoo:{value(){return this.foo}}})
  myObj.foo = 'bar'
  console.log(Object.entries(myObj)) // [ ['foo','bar'] ]

  console.log(Object.entries('foo')) //[ ['0','f'],['1','o'],['2','o'] ]

  const obj2 = {a:5,b:7,c:9}
  for(const [key,value] of Object.entries(obj)){
      console.log(`${key} ${value}`) // " a 5","b 7","c 9"
  }

  Object.entries(obj2).forEach(([key,value])=>{
      console.log(`${key} ${value}`) // " a 5","b 7","c 9"
  })