手写js原生API训练场

为什么写这个？因为好玩。没事做就写着打发时间。

Function

Function.prototype.call

Function.prototype._call = function(_this){
    const ctx = _this || window
    const sym = Symbol('call_ctx')
    const args = [...arguments]
    args.shift()
    ctx[sym] = this
    const res = ctx[sym](...args)
    delete ctx[sym]
    return res
}
// test
const a = function(b,c){
    console.log(this.a,b);
    return c 
}
const o = {a:1};
a._call(o,'b',['c']) // console 1,'b' return ['c']
console.log(o) // { a:1 }

Function.prototype.bind

Function.prototype._bind = function(_this){
	const ctx = _this || window
	const args = [...arguments].slice(1)
    const instance = this
	return function F(){
        if(this instanceof F){
            return new instance(...args,...arguments)
        }
		return instance.apply(_this,args.concat(...arguments))
	}
}

Array

Array.prototype.push

Array.prototype._push = function(){
    const l = this.length
    const args = arguments
    for(let i=0,len=args.length;i<len;i++){
        this[l+i] = args[i]
    }
    return this.length
}

Array.prototype.pop

Array.prototype._pop = function(){
    const l = this.length
    if(l){
        const value = this[l-1]
        this.length = l-1
        return value
    }
    return undefined
}

Array.prototype.forEach

Array.prototype._forEach = function(fn,_this){
    const len = this.length
    let i = 0
    while(i<len){
        fn.call(_this,this[i],i,this)
        i++
    }
}

Array.prototype.map

Array.prototype._map = function(fn,_this){
    const len = this.length
    const arr = []
    let i = 0
    while(i<len){
        arr.push(fn.call(_this,this[i],i,this))
        i++
    }
    return arr
}

Array.prototype.filter

Array.prototype._filter = function(fn,_this){
    const len = this.length
    const arr = []
    let i = 0
    while(i<len){
        const res = fn.call(_this,this[i],i,this)
        res && arr.push(this[i])
        i++
    }
    return arr
}

Array.prototype.some

Array.prototype._some = function(fn,_this){
	const len = this.length
    if(len===0)return false
	let i = 0
	let result = false
	while(i<len){
		if(fn.call(_this,this[i],i,this)){
			result = true
			break
		}
		i++
	}
	return result
}

Array.prototype.every

Array.prototype._every = function(fn,_this){
	const len = this.length
    if(len===0)return false
	let i = 0
	let result = true
	while(i<len){
		if(!fn.call(_this,this[i],i,this)){
			result = false
			break
		}
		i++
	}
	return result
}

Array.prototype.reverse

Array.prototype._reverse = function(){
	const len  = this.length
	const mid = parseInt(len/2)
	for(let i=0;i<mid;i++){
		const temp = this[i]
		this[i] = this[len-i-1]
		this[len-i-1] = temp
	}
	return this
}

Promise

按照Promise/A+ (opens new window)规范。