如何取消设置数组中的条目？

Question

If I declare a new Array() and add a value, but then I want to remove that value, how do I do so? Setting the value = null simply creates a null value at that index, while removing that index with splice reduces the size of the array. See below:

class CustomArray {
  constructor(size) {
    this.arr = new Array(size)
  }

  describe() {
    console.log(this.arr.length)
    this.arr.forEach(num => console.log(num))
  }

  insert(idx, val) {
    this.arr.splice(idx, 1, val)
  }

  remove(idx) {
    this.arr[idx] = null
  }

  remove2(idx) {
    this.arr.splice(idx, 1)
  }

}

let myArr = new CustomArray(20)
myArr.insert(3, 100)
myArr.remove(3)
myArr.describe() //outputs 20 for length and `null`


let mySecondArr = new CustomArray(20)
mySecondArr.insert(3, 100)
mySecondArr.remove(3) //ouputs 19 for length

//how do I remove all values AND retain length?

Answer 1

You can use delete operator. delete will create an empty slot at that particular index. According to MDN

When you delete an array element, the array length is not affected . This holds even if you delete the last element of the array.

 class CustomArray { constructor(size) { this.arr = new Array(size) } describe() { console.log(this.arr.length) this.arr.forEach(num => console.log(num)) } insert(idx, val) { this.arr.splice(idx, 1, val) } remove(idx) { delete this.arr[idx] } remove2(idx) { this.arr.splice(idx, 1) } } let myArr = new CustomArray(20) myArr.insert(3, 100) myArr.remove(3) myArr.describe() 

Answer 2

I believe delete arr[i] is what you're looking for. The length of the array doesn't change, the value is set to undefined, but it is also ignored by functions such as map and forEach , so they never run code for a deleted value.