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);
});