ES6对象方法的扩展详解

阅读目录

Object.assign(target, source_1, ···)

概念:方法用于对象的合并,将源对象(source)的所有可枚举属性,复制到目标对象(target)

特点:为对象添加属性和方法、克隆对象、合并多个对象、为属性指定默认值

案例:

var sourceObj1 = {
    name:"assign"
}
var sourceObj2 = {
    age:"18"
}
var target = {};
Object.assign(target, sourceObj1, sourceObj2); 
console.log(target); //{name: "assign", age: "18"}

//目标对象与源对象有同名属性,或多个源对象有同名属性,则后面的属性会覆盖前面的属性
var sourceObj3 = {
    name:"assign1"
}
var target1 = {};
Object.assign(target1, sourceObj1, sourceObj3);
console.log(target1); //{name: "assign1", age: "18"}

//源对象为字符串则会拷贝其枚举属性,数值和布尔值不会产生效果

var sourceString = "assign";
var target2 = {};
Object.assign(target2, sourceString, true, 18);
console.log(target2); //{0: "a", 1: "s", 2: "s", 3: "i", 4: "g", 5: "n"}

//只有字符串的包装对象,会产生可枚举的实义属性,那些属性则会被拷贝 [[PrimitiveValue]]不会被Object.assign拷贝
console.log(Object(sourceString)); //{0: "a", 1: "s", 2: "s", 3: "i", 4: "g", 5: "n",length:6,[[PrimitiveValue]]:assign}

//Object.assign拷贝的属性是有限制的,只拷贝源对象的自身属性,不拷贝不可枚举的属性,不拷贝继承属性
var target3 = {};
Object.assign(target3,
  Object.defineProperty({}, 'name', {
    enumerable: false,
    value: 'hello'
  }),
  Object.defineProperty({}, 'age', {
    enumerable: true,
    value: 18
  })
)
console.log(target3); //{age:18}

//Object.assign方法实行的是浅拷贝,而不是深拷贝
//如果源对象某个属性的值是对象,那么目标对象拷贝得到的是这个对象的引用
var target4 = {};
sourceObj4 = {name:{value:"assign"}};
Object.assign(target4, sourceObj4);
sourceObj4.name.age = 18;
console.log(target4); //{name:{value:"assign",age:18}};
</script>

Object.is(value1, value2)(object, descriptors)

概念:判断两个值是否是相同的值

案例:

Object.is(window,window); //true
Object.is({name:"is"},{name:"is"}); //false
Object.is([],[]); //false
Object.is(undefined,undefined); //true
Object.is(null,null);  
Object.is(0, -0);  // false
Object.is(-0, -0);  // true
Object.is(NaN, 0/0);  // true

Object.setPrototypeOf(object)

概念:修改一个对象的内置属性[[Prototype]]

注:该方法影响性能,避免使用,可以使用Object.create代替

var obj = {};
var obj1 = {name:"setPrototypeOf"};
Object.setPrototypeOf(obj, obj1);
console.log(obj.name); //"setPrototypeOf"

//模拟new命令
var F = function () {};
var f = Object.setPrototypeOf({}, F.prototype);
F.call(f);
// 等同于
var f = new F();

Object.getPrototypeOf(object)

概念:返回参数对象的原型

案例:

var F = function () {};// 构造函数
var f = new F();
Object.getPrototypeOf(f) === F.prototype // true

// 空对象的原型是 Object.prototype
Object.getPrototypeOf({}) === Object.prototype // true

// Object.prototype 的原型是 null
Object.getPrototypeOf(Object.prototype) === null // true

// 函数的原型是 Function.prototype
function f() {}
Object.getPrototypeOf(f) === Function.prototype // true

 

posted @ 2019-07-30 14:31  yaolan  阅读(255)  评论(0编辑  收藏  举报