JS 底层手动实现 forEach map filter

定义公共数组

const arr=[{name:"张三",age:19},{name:"李四",age:22},{name:"王五",age:30}]

ForEach实现方法

Array.prototype.ljy_forEach=function(callback){
	   for(let i=0;i<this.length;i++){
        callback(this[i],i,arr)
     }
}
arr.ljy_forEach((item,index,arr)=>{console.log(item,index,arr)})

map实现方法

Array.prototype.ljy_map= function (callback) {
    const res = []
    for (let i = 0; i < this.length; i++) {
        res.push(callback(this[i], i, this))
    }
    return res
}
	  console.log(arr.ljy_map((item,index)=>{console.log(item,index)})))

filter实现方法

Array.prototype.sx_filter = function (callback) {
    const res = []
    for (let i = 0; i < this.length; i++) {
        callback(this[i], i, this) && res.push(this[i])
    }
    return res
}

console.log(players.sx_filter(item => item.num >= 23))