filter，map用法

filter也是一个常用的操作，它用于把Array的某些元素过滤掉，然后返回剩下的元素。和map()类似，Array的filter()也接收一个函数。和map()不同的是，filter()把传入的函数依次作用于每个元素，然后根据返回值是true还是false决定保留还是丢弃该元素。filter return的是筛选条件，map return的是计算结果

filter筛选过滤

<script type="text/javascript">
    var array = [
          {'number':1},
          {'number':2},
          {'number':3},
          {'number':4},
          {'number':5}
     ];
    var array_filter = array.filter(function(element,index,self){
            console.log(element);     // 依次打印子项'{'number':1}','{'number':2}'... 
            console.log(index);         //依次打印下标0,1,2,3 
            console.log(self);            // 打印数组array 
            return element.number < 3;
      });
      console.log(array_filter);
      // 打印 [{'number':1}, {'number':2}] 
 </script>

map计算生成新数组

<script type="text/javascript">
    var array = [
          {'number':1},
          {'number':2},
          {'number':3},
          {'number':4},
          {'number':5}
     ];
    var array_map = array.map(function(element,index,self){
            console.log(element);     // 依次打印子项'{'number':1}','{'number':2}'... 
            console.log(index);         //依次打印下标0,1,2,3 
            console.log(self);            // 打印数组array 
           element.number = element.number * 3;
            return element;
      });
      console.log(array_map);
      // 打印 [{'number':3}, {'number':6},{'number':9}, {'number':12}, {'number':15}] 
 </script>