原生JS forEach()和map()遍历的区别、兼容写法及jQuery $.each、$.map遍历操作

var ary = [12,23,24,42,1];var res = ary.forEach(function (item,index,input) {    input[index] = item*10;})console.log(res);//-->undefined;console.log(ary);//-->会对原来的数组产生改变

var ary = [12,23,24,42,1];var res = ary.map(function (item,index,input) {  return item*10;})console.log(res);//-->[120,230,240,420,10];console.log(ary);//-->[12,23,24,42,1]

/*** forEach遍历数组* @param callback [function] 回调函数；* @param context [object] 上下文；*/Array.prototype.myForEach = function myForEach(callback,context){  context = context || window;  if('forEach' in Array.prototye) {    this.forEach(callback,context);    return;  }  //IE6-8下自己编写回调函数执行的逻辑  for(var i = 0,len = this.length; i < len;i++) {    callback && callback.call(context,this[i],i,this);  }}

/*** map遍历数组* @param callback [function] 回调函数；* @param context [object] 上下文；*/Array.prototype.myMap = function myMap(callback,context){  context = context || window;  if('map' in Array.prototye) {    return this.map(callback,context);  }  //IE6-8下自己编写回调函数执行的逻辑  var newAry = [];  for(var i = 0,len = this.length; i < len;i++) {    if(typeof callback === 'function') {      var val = callback.call(context,this[i],i,this);      newAry[newAry.length] = val;    }  }  return newAry;}

$.each( ["a","b","c"], function(i, n){   alert( i + ": " + n );});

$("span").each(function(i, n){   alert( i + ": " + n );});

$.each( { name: "John", lang: "JS" }, function(k, n){   alert( "Name: " + k + ", Value: " + n );});

var arr=$.map( [0,1,2], function(n){   return n + 4;});console.log(arr);

$.map({"name":"Jim","age":17},function(i,n){   console.log(i+":"+n);});