如何在JavaScript中检查null值？ [英] How do I check for null values in JavaScript?

问题描述

如何在JavaScript中检查null值？我写了下面的代码，但它没有工作。

How can I check for null values in JavaScript? I wrote the code below but it didn't work.

if (pass == null || cpass == null || email == null || cemail == null || user == null) {      

    alert("fill all columns");
    return false;  

}   

如何在我的JavaScript程序中找到错误？ / p>

And how can I find errors in my JavaScript programs?

推荐答案

Javascript对于检查null值非常灵活。我猜你真的在寻找空字符串，在这种情况下，这个更简单的代码将工作：

Javascript is very flexible with regards to checking for "null" values. I'm guessing you're actually looking for empty strings, in which case this simpler code will work:

if(!pass || !cpass || !email || !cemail || !user){

对于空字符串（）， null ， undefined ， false 和数字 0 和 NaN

Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN

请注意，如果你是专门检查数字，这是一个常见的错误，错过 0 使用此方法， c $ c> num！== 0 是首选（或 num！== -1 或〜num -1 的函数的code> indexOf ）

Please note that if you are specifically checking for numbers it is a common mistake to miss 0 with this method, and num !== 0 is preferred (or num !== -1 or ~num (hacky code that also checks against -1)) for functions that return -1, e.g. indexOf)

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