js手写数组push(),unshift(),pop(),shift(),map()方法_js手写unshift

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 undefined
    const 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 undefined
    const 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
    
}))