语法:
_.each(list, iteratee, [context])
说明：
依次对集合的所有元素进行某种操作，原样返回list。接收3个参数，list集合可以理解为数据源；iteratee即迭代器可以理解为回调方法;context执行上下文。
- list可以为数组，对象，字符串和arguments
- iteratee 会传第三个参数(element, index, list)或(value, key, list)
- context可以改变iteratee内部的this
示例一：each可以循环数组、对象、字符串和arguments
//遍历数组_.each([1, 2, 3], function (element, index, list) { ???console.log(element);});//遍历对象_.each({one: ‘一‘, two: ‘二‘, three: ‘三‘}, function(value, key, list){ ???console.log(value);});//遍历字符串_.each(‘123‘, function(element, index, list){ ???console.log(element);});//遍历argumentsfunction abc(){ ???_.each(arguments, function(element, index, list){ ??????console.log(element); ???});}abc(1, 2, 3);示例二：iteratee传递的参数
//数组的情况_.each([1, 2, 3], function (element, index, list) { ???console.log(element, index, list); ???//1 0 [1, 2, 3] ???//2 1 [1, 2, 3] ???//3 2 [1, 2, 3]});//对象的情况_.each({one: ‘一‘, two: ‘二‘, three: ‘三‘}, function(value, key, list){ ???console.log(value, key, list); ???//一 one Object {one: "一", two: "二", three: "三"} ???//二 two Object {one: "一", two: "二", three: "三"} ???//三 three Object {one: "一", two: "二", three: "三"}});示例三：context可以改变iteratee内部的this
_.each([1], function (element, index, list) { ???console.log(this); //window});_.each([1], function (element, index, list) { ???console.log(this); //{key: 1}}, {key : 1});示例四：each的返回值
var arr1 = _.each([1, 2, 3], function (element, index, list) {});var arr2 = _.each({one: ‘一‘, two: ‘二‘, three: ‘三‘}, function(element, index, list){});console.log(arr1); //[1, 2, 3]console.log(arr2); //Object {one: "一", two: "二", three: "三"}_.forEach的功能和_.each是一样的
_.forEach([1, 2, 3], function (element, index, list) { console.log(element); });
遍历非集合（遍历特殊值都不会报错，但也不执行。在遍历一个集合的时候，最好能先确定他是数组或对象等。）
_.each(null, function (element, index, list) { ???console.log(element); //不执行});_.each(undefined, function (element, index, list) { ???console.log(element); //不执行});_.each(123, function (element, index, list) { ???console.log(element); //不执行});_.each(new Date(), function (element, index, list) { ???console.log(element); //不执行});iteratee还可以是全局的方法
_.each([1, 2, 3], alert); //会弹三次
underscorejs类库之_.each(list, iteratee, [context])
原文地址：http://www.cnblogs.com/rechel/p/7615040.html