【前端面试：手写js系列】数组的map方法和forEach方法

• Array.prototype.map()

map方法参数说明

let arr = [3, 4, 5, 6, 7];

Array.prototype.mapArray = function ( fn, thisArgs ){
//处理数组类型异常
    if (this === null || this === undefined){
        throw new TypeError("Cannot read property 'map' of null or undefined ");
    }
//处理回调函数异常   
    if (object.prototype.toString.call(fn) !== "[object Function]") {
        throw new TypeError(fn + 'is not a function')
    }
    let resArray = [ ];
    let curArray = Object(this);
    let len = curArray.length >>> 0;

    for (let i = 0; i < curArray.length; i++){
        if (i in curArray){
            resArray[ i ] = fn.call(thisArgs, curArray[ i ], i, curArray);
        }
    }
    return resArray;
}

console.log(arr.mapArray((item, index, arr) => {return item + 1}));
//[4, 5, 6, 7, 8]

• Array.prototype.forEach()

forEach方法和map方法类似，唯一不同的是forEach没有返回值。

forEach方法参数说明

//forEach方法和map方法类似，唯一不同的是forEach没有返回值
Array.prototype.forEach = function(callback, thisArgs){
    if( this === null || this === undefined){
        throw new TypeError("this is null or not defined");
    }
    if( object.prototype.toString.call(callback) !== "[object function]"){
        throw new TypeError(callback+"is not a function");
    }
    let curArr = Object(this);
    let len = curArr.length >>> 0;
    let i = 0;
    while( i < len){
        if (i in curArr){
            callback.call(thisArgs, curArr[i], i, curArr);
        }
        i++;
    }
}