Javascript test for null

In general, null and undefined both mean the same thing: "something's missing". For predictability, you need to check both values. In exceptional cases you do want a clear distinction between null and undefined.

But it is rare. It is not only rare, it's something to avoid. You can't store undefined in a traditional database. And you shouldn't rely on undefined values in your API designs neither, due to interopability reasons. But even when you don't make a distinction at all, you can't assume that undefined won't happen.

So, to get back to your question. It does exactly what it should do. Improvement over the accepted answer by explicitly checking for null but with a simplified syntax:. Firstly, you have a return statement without a function body. Chances are that that will throw an error. See this. Given that '' and 0 are loosely equal, you might reasonably conjecture that '' and null are loosely equal.

However, they are not. The result of comparing any string to null is false. On the other hand, some experts say that it's a good practice to always use strict equality in JavaScript unless you specifically want to do the type coercion that the loose equality operator performs.

If you want to know what pairs of values are loosely equal, see the table "Sameness comparisons" in the Mozilla article on this topic. Actually I think you may need to use if value! In my situation, I just needed to check if the value is null and undefined and I did not want to filter 0 or false or '' values. This is a comment on WebWanderer's solution regarding checking for NaN I don't have enough rep yet to leave a formal comment.

The solution reads as. A better test would be:. But as null is also an object we can detect it as a null. I made a more complex function natureof witch will do better than typeof and can be told what types to include or keep grouped.

The route is whatever chain of values that can blow up. Of course if you prefer you can use null or 'No value' Whatever suit your needs.

Usually a DOM query or a jQuery selector may throw an error if it's not found. But using something like:. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Collectives on Stack Overflow. Learn more. How do I check for null values in JavaScript? Ask Question. Asked 10 years, 8 months ago. Active 24 days ago. Viewed 1.

How can I check for null values in JavaScript? I wrote the code below but it didn't work. Improve this question. Are you sure the values you are testing are actually null and not just empty string?

Check out my wording, I'm clearly making a general statement about the language in reference to the OP's practise, and not proposing that this solves his problem.

TRiG the proposed changes fundamentally alter the nature of the question to the point where the answers not just mine lose context and don't make sense. The edit should just be a comment. Show 2 more comments. Active Oldest Votes. I'm guessing you're actually looking for empty strings, in which case this simpler code will work: if!

Improve this answer. Matthias Braun Nobody Nobody Instead of returning a null when the argument is missing, return a default:. Typically, when a developer declares a variable less an initial value, the variable will always evaluate to undefined when they try to access it. The significant difference between undefined and null is that null shows a missing object while undefined represents an uninitialized state. Again, some developers may use this operator to check whether a variable is undefined or null.

However, the tricky part is it mainly treats them as similar. So, the superior way of checking for a null in JavaScript is through performing a strict equality comparison against a null keyword and then pass both values. Save my name, email, and website in this browser for the next time I comment. Sign in. Log into your account. Forgot your password? Password recovery. Recover your password. Friday, January 14, Get help.

Position Is Everything. Three methods can help you check for null in JavaScript. This operator can check for null and undefined at the same time. Table of Contents. Author Recent Posts. Position is Everything.

Latest posts by Position is Everything see all. Please enter your comment! Please enter your name here. You have entered an incorrect email address! Position is Everything - November 19, 0. If object is truthy, we already know that it is not null or undefined assuming that the string values are a mistake.

I assume that a not null and not undefined test is wanted. If so, a simple comparison to null or undefined is to compare! The doSomething function will run only if object is neither null nor undefined.

However, if you first check that object! You can use eval to cast any type including string and be executed by javascript, here is eval documentation. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 9 years, 3 months ago.

Active 1 month ago. Viewed 96k times. Improve this question. Nick G. If it actually may have the string values "null" and "undefined" , then your method can't be any simpler. It does sometimes have the strings "null" or "undefined". Thanks for the confirmation. You can also use!! It converts the object to boolean and then inverts it again. Look at this answer for a very good explanation. Add a comment. Active Oldest Votes. Improve this answer.

John 11k 11 11 gold badges 82 82 silver badges bronze badges.