为什么我不能使用绑定方法清空 class 中的数组？

Question

Below I have the Example class with two bound methods reset and addItem . I'd expected this code to log 0 but instead it logs 4 . I'm curious as to why this is happening, and if there is a way to have it work the way I'd expect.

 class Example { array = [] constructor () { this.reset = this.reset.bind(this) this.addItem = this.addItem.bind(this) } reset () { this.array = [] } addItem () { this.array.push('hello') } } const {array, reset, addItem} = new Example() addItem() addItem() addItem() addItem() reset() console.log(array.length)

Answer 1

In this line

const {array, reset, addItem} = new Example()

you're extracting the current references of array , reset , and addItem when the object is instantiated. If you reassign one of the properties of the object later, the previous references will not change by themselves to point to the new value. For the same reason, the following logs 1, not 2.

 const obj = { num: 1 }; let { num } = obj; obj.num = 2; console.log(num);

For your code, you could make a method named getArray

 class Example { array = [] constructor () { this.reset = this.reset.bind(this) this.addItem = this.addItem.bind(this) } getArray = () => this.array; reset () { this.array = [] } addItem () { this.array.push('hello') } } const {getArray, reset, addItem} = new Example() addItem() addItem() addItem() addItem() reset() console.log(getArray().length)

Or you could mutate the array instead of reassigning it in reset .

 class Example { array = [] constructor () { this.reset = this.reset.bind(this) this.addItem = this.addItem.bind(this) } reset () { this.array.length = 0; } addItem () { this.array.push('hello') } } const {array, reset, addItem} = new Example() addItem() addItem() addItem() addItem() reset() console.log(array.length)