目录

1、push()

2、unshift()

3、pop()

4、shift()

5、map()

---

1、push()

        Array.prototype.push=function(){for(let i=0;i<arguments.length;i++){this[this.length]=arguments[i]}return this.length}const arr=[1,2,3]console.log(arr.push(4,5,6))

2、unshift()

  Array.prototype.unshift = function () {const args = [...arguments]const oldArray = [...this]for (let i = 0; i < args.length; i++) {this[i] = args[i]}for (let j = 0; j < oldArray.length; j++) {this[this.length] = oldArray[j]}return this.length}const arr = [1, 2, 3]console.log(arr.unshift(6, 5, 4))

3、pop()

Array.prototype.pop=function(){if(this.length===0)return undefinedconst lastItem=this[this.length-1]this.length--return lastItem
}
const arr=[1,3,4]
console.log(arr.pop())

4、shift()

Array.prototype.shift=function(){if(this.length===0)return undefinedconst firstItem=this[0]for(let i=0;i<this.length;i++){this[i-1]=this[i]}this.length--return firstItem
}
const arr=[1,2,3]
console.log(arr.shift())

5、map()

Array.prototype.map=function(fn){const newArr=[]for(let i=0;i<this.length;i++){const r=fn(this[i],i,arr)newArr[newArr.length]=r}return newArr
}
arr=[8,5,7,9]
console.log(arr.map(function(item){return item*2}))