过滤数组 Filtering Arrays

## 问题 Problem 你想基于某个布尔条件来过滤数组。 You want to be able to filter arrays based on a boolean condition. ## 方法 Solution 使用`Array.filter`（ECMAScript 5）: Use Array.filter (ECMAScript 5): ~~~ array = [1..10] array.filter (x) -> x > 5 # => [6,7,8,9,10] ~~~ 在pre-EC5的实现中，给Array的原型扩展一个过滤函数，这个函数接受一个回调函数，并迭代整个数组，收集所有调用过滤函数的为true的元素。在复写这个函数的之前需要先确保这个是否已经实现了： In pre-EC5 implementations, extend the Array prototype to add a filter function which will take a callback and perform a comprension over itself, collecting all elements for which the callback is true. Be sure to check if the function is already implemented before overwriting it: ~~~ # Extending Array's prototype unless Array::filter Array::filter = (callback) -> element for element in this when callback(element) array = [1..10] # Filter odd elements filtered_array = array.filter (x) -> x % 2 == 0 # => [2,4,6,8,10] # Filter elements less than or equal to 5: gt_five = (x) -> x > 5 filtered_array = array.filter gt_five # => [6,7,8,9,10] ~~~ ## 讨论 Discussion 这个方法的用法与Ruby中Array的select方法类似。 This is similar to using ruby’s Array#select method.