JavaScript对象函数和`this`在未绑定并在表达式/ parens中返回时 [英] JavaScript object functions and `this` when unbound and returned in expression/parens

问题描述

第1-2和4-5行在返回此方面有意义。关于第3行，我错过了什么？我认为它会返回窗口，类似于4-5行。是否还有另外一种模式可以帮助证明原因？

Lines 1-2 and 4-5 make sense in terms of the this returned. What am I missing about line 3? I thought it would return window similar to lines 4-5. Is there another pattern not in these 5 that could help demonstrate why?

foo = { bar : function () { return this } }

foo.bar() // ==> foo

(foo.bar)() // ==> foo / but why?

(foo.bar ? foo.bar : $.noop)() // ==> window

(foo.bar || 0)() // ==> window

推荐答案

分组运算符不会破坏属性引用，正在激发方法调用。

The grouping operator does not destroy property references, which are provoking the method call.

这在规范：

注意：此算法不适用 GetValue 到
评估 Expression 的结果。这样做的主要动机是可以将
运算符（如 delete 和 typeof ）应用于带括号的
表达式。

NOTE: This algorithm does not apply GetValue to the result of evaluating Expression. The principal motivation for this is so that operators such as delete and typeof may be applied to parenthesised expressions.

在第4行和第5行中，它不是括号而是运算符（？ ：和 || ）取消引用该属性并生成未绑定函数。

In your lines 4 and 5, it's not the parenthesis but the operators (?: and ||) that de-reference the property and yield the "unbound" function.

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