检查JavaScript变量是否为空的最可靠方法是什么？ [英] What's the most reliable way to check if a JavaScript variable is null?

问题描述

如果我想检查变量是否为空或不存在，那么可靠的方法是什么？

What is the mos reliable way if I want to check if the variable is null or is not present?.

有不同的例子：

if (null == yourvar)

if (typeof yourvar != 'undefined')

if (undefined != yourvar)

推荐答案

以上都不是。

你不想用 == 或其中的各种因为它执行类型强制。如果你真的想检查是否显式为null，请使用 === 运算符。

You don't want to use ==, or a variety thereof, because it performs type coercion. If you really want to check whether something is explicitly null, use the === operator.

然后，您的问题可能显示您的要求缺乏明确性。你具体是指 null 吗？或未定义计数？ myVar === null 肯定会告诉你变量是否为空，这是你问的问题，但这真的是你想要的吗？

Then again, your question shows perhaps some lack of clarity of your requirements. Do you actually mean null specifically; or does undefined count too? myVar === null will certainly tell you if the variable is null, which is the question you asked, but is this really what you want?

请注意，这个问题。它不是直接复制，但它涵盖了非常相似的原则。

Note that there's a lot more information in this SO question. It's not a direct duplicate, but it covers very similar principles.

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