Array

 const strings = ['a', 'b', 'c', 'd'];
strings[2] //O(1)

//push 数组末尾加，O(1),不循环，直接找到
strings.push('e') 
//结果:(5) ['a', 'b', 'c', 'd', 'e']

//pop  删除末尾最后一个元素，O(1),不循环
strings.pop()
//结果:(4) ['a', 'b', 'c', 'd']

//unshift 数组开头添加元素，O(n)，循环，数组原数据移动
strings.unshift('x')
//(5) ['x', 'a', 'b', 'c', 'd']

//splice 通过删除或替换现有元素或者原地添加新的元素来修改数组,并以数组形式返回被修改的内容。此方法会改变原数组   O(n)

strings.splice(2,0,'alien')
//结果:(5) ['a', 'b', 'alien', 'c', 'd']
strings.splice(2,1,'alien')
//结果:(4) ['a', 'b', 'alien', 'd']

console.log(strings)

手动创建一个数组类

class MyArray{
  constructor(){
    this.length = 0;
    this.data = {}
  }
  get (index){
    return this.data[index];
  }
  push(item){
    this.data[this.length] = item;
    this.length ++
    return this.data;
  }
  pop(){
    const lastItem = this.data[this.length -1];
    delete this.data[this.length - 1];
    this.length --;
    return lastItem;
  }
  deleteAtIndex(index){
    const item = this.data[index];
    this.shiftItems(index);
    return item;
  }
  shiftItems(index){
    for(let i = index;i<this.length-1;i++){
      this.data[i] = this.data[i+1];
    }
    delete this.data[this.length-1];
    //console.log(this.data);
    this.length--;
  }
  shift(){
    const firstItem = this.data[0];
    this.shiftItems(0);
    return firstItem;
  }
  unshift(...funs){

  }
}

const myArray = new MyArray();
myArray.push('I');
myArray.push('am');
myArray.push('are');
myArray.push('you');
console.log(myArray)
//myArray.deleteAtIndex(1)
myArray.shift();
console.log(myArray)