Object in ES6

Equality

tip

• equality in JavaScript ES5 using '==' and '==='; and introduction to the Object.is() method in ES6, which is very similar to '==='
• == will compare the values.
• === will compare the values and the types. :::

the difference between === and Object.is(x,y)

console.log(Object.is(+0, -0)) // is `false`, while
console.log(-0 === +0) // is `true`

Object.is(NaN, NaN) // is `true`, while
console.log(NaN === NaN) // is false

Mixins with Object.assign(a,b)

let horse = {
  horseName: "QuickBucks",
  toString: function () {
    return this.horseName
  }
}

let rider = {
  riderName: "Frank",
  toString: function () {
    return this.riderName
  }
}

let horseRiderStringUtility = {
  toString: function () {
    return this.riderName + " on " + this.horseName
  }
}

// mixins all of the object above.
let racer = Object.assign(
  {}, // It's better to add an empty object, otherwise the horse will be mutated(changed).
  horse,
  rider,
  horseRiderStringUtility
)

console.log(racer.toString()) // The output is : Frank on QuickBucks

Object Prototype Extensions and Super Calls

• first the prototype of obj is {}
• when we invoke setPrototypeOf(obj, proto), the prototype of obj becomes proto
• so finally we change the parent object of the obj. :::

let proto = {
  whoami() {
    console.log("I am proto")
  }
}

let obj = {
  whoami() {
    super.whoami()
    console.log("I am obj")
  }
}

console.log(Object.getPrototypeOf(obj))
//{}

Object.setPrototypeOf(obj, proto)

obj.whoami()
// I am proto
// I am obj

defineProperty

const obj = {
  x: 1,
  y: 2
}

console.log(obj)

/**
    configurable: 是否可删除
    enumerable: 是否可迭代
    writable: 是否可修改
    value: 数值

    {
        x: { value: 1, writable: true, enumerable: true, configurable: true },
        y: { value: 2, writable: true, enumerable: true, configurable: true }
    }

 */
console.log(Object.getOwnPropertyDescriptors(obj))

Object.defineProperty(obj, "x", {
  configurable: false, // 不能删
  writable: false, // 不能改
  enumerable: false // 不能迭代
})

// delete obj.x
obj.x = 10

console.log(obj)

// get set方法劫持
Object.defineProperty(obj, "y", {
  get() {
    console.log("get value")
    return 0
  },
  set() {
    console.log("set value")
  }
})

console.log(obj.y)
obj.y = 100