手写实现Array.prototype.map/filter/reduce

[HelenHai]

Array.ptototype.map

Array.prototype.map1 = function(fn) {
    let arr = []

    for(let i=0; i<this.length; i++) {
        arr.push(fn(this[i]))
    }
    return arr
}

Array.ptototype.filter

Array.prototype.filter1 = function(fn) {
    let arr = []

    for(let i=0; i<this.length; i++) {
        fn(this[i]) && arr.push(this[i])
    }
    return arr
}

Array.ptototype.reduce

Array.prototype.reduce1 = function(fn, initial) {
    for(let i=0; i<this.length; i++) {
        initial = fn(initial, this[i], i, this)
    }
    return initial
}

references

1. for 循环不是目的，map 映射更有意义！