_.each（list，iterator，[context]）中的上下文是什么？ [英] What is context in _.each(list, iterator, [context])?

问题描述

我是underscore.js的新手。 _。each（）中的 [context] 的用途是什么？它应该如何使用？

解决方案

context参数设置这个值


  var someOtherArray = [name，patrick，d，w ]; 
 
_each（[1，2，3]，function（num）{
 //在这里，this指向与someOtherArray相同的数组
 
 alert（this [num]）; // num是被迭代的数组的值
 //所以这个[num]获得
 //的num索引处的项目someOtherArray。
}，someOtherArray）; 
  

工作示例 http://jsfiddle.net/a6Rx4/

它使用数组中每个成员的数字迭代获得 someOtherArray 索引的项目，该项目由 this 表示，因为我们将其作为上下文传递给它如果你没有设置上下文，那么这个会引用参数。窗口对象。

I am new to underscore.js. What is the purpose of [context] in _.each()? How should it be used?

解决方案

The context parameter just sets the value of this in the iterator function.

var someOtherArray = ["name","patrick","d","w"];

_.each([1, 2, 3], function(num) { 
    // In here, "this" refers to the same Array as "someOtherArray"

    alert( this[num] ); // num is the value from the array being iterated
                        //    so this[num] gets the item at the "num" index of
                        //    someOtherArray.
}, someOtherArray);

Working Example: http://jsfiddle.net/a6Rx4/

It uses the number from each member of the Array being iterated to get the item at that index of someOtherArray, which is represented by this since we passed it as the context parameter.

If you do not set the context, then this will refer to the window object.

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