Array.from

可参考 MDN 里的 Array.from

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/from

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var obj = {  0:1, 1:2, 2:3,
           length:3, // 1
           length:4, // 2
           length:0, // 3
           push:[].push //可在对象中定义数组方法
          };
obj -> 伪类 ->类似于数组的一种伪类型 -> 不是JS类型
var newArr = Array.from(obj);
console.log(newArr);
// 1: [1,2,3]; 2:[1,2,3,unfeined]; 3: []
//length决定了Array.from最终返回的新数组的长度，剪裁掉或补齐 (undiefined)
console.log(newArr.length);
obj.push(4);
console.log(obj);// [1,2,3,4]

Funny reference val

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`function Array Object -> 引用值 ->Object.prototype`;
var obj1 = {};
obj1.a = 1;
var newObj = new Object(obj1); //  newObj = obj1;
console.log(newObj === obj1); //true | {a:1} - {a:1}

var arr1 = [1, 2, 3, 4];
console.log(new Object(arr1)); // [1,2,3,4]

var arr = [];
arr.a = 1;
var newarr = new Array(arr);
console.log(newarr == arr); //false | [a:1] - [Array(0)] : 0-> [a:1]

var str = '123'; // 原始值
console.log(str.__proto__); //原始类型

var a = 1; // 原始值
var newA = new Number(a); //引用值
console.log(a == newA); //true | 隐式类型转换
console.log(a === newA); //false | 1 - Number{1}

Object

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var obj ={
    a:1,
    b:2,
    c:3
}
Object.defineProperty(obj,'b'{
    enumerable:false
})
// 应用场景不一样
console.log(Object.keys(obj));
// 忽略描述符 -enumerable:false
console.log(Object.getOwnPropertyNames(obj));