什么是Javascripts的语义如果声明 [英] What Are the Semantics of Javascripts If Statement

问题描述

我一直认为if语句基本上比较了它的类似于 == true 的参数。然而，Firebug中的以下实验证实了我最糟糕的恐惧 - 在写了15年的Javascript后我仍然没有任何线索WTF正在进行中：

I always thought that an if statement essentially compared it's argument similar to == true. However the following experiment in Firebug confirmed my worst fears—after writing Javascript for 15 years I still have no clue WTF is going on:

>>> " " == true
false
>>> if(" ") console.log("wtf")
wtf

我的世界观是在这里乱糟糟的。我可以运行一些实验来了解更多信息，但即使这样，我也会因为害怕浏览器怪癖而失眠。这是某个规格吗？它是否一致的跨浏览器？我会掌握javascript吗？

My worldview is in shambles here. I could run some experiments to learn more, but even then I would be losing sleep for fear of browser quirks. Is this in a spec somewhere? Is it consistent cross-browser? Will I ever master javascript?

推荐答案

如果两个操作数不是同一类型，JavaScript会转换操作数然后应用严格如果操作数是数字或布尔值，则操作数将转换为数字;如果任一操作数是字符串，则另一个操作数转换为字符串。

"If the two operands are not of the same type, JavaScript converts the operands then applies strict comparison. If either operand is a number or a boolean, the operands are converted to numbers; if either operand is a string, the other one is converted to a string."

https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Operators / Comparison_Operators

所以第一个做：

Number(" ")==Number(true)

虽然第二个评估如下：

While the second one is evaluated like this:

if(Boolean(" ")==true) console.log("wtf")

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