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:. How are we doing? Please help us improve Stack Overflow. Take our short survey. 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. 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! Matthias Braun Nobody Nobody It would be very useful to know which parts of this test for which values. Sometimes you're looking for one in particular. Somewhat of a late statement, but yes, you can perform test against each one inorganik , see my answer below — WebWanderer.
Readers, please be careful when using this type of test on numeric data. Do not use! The answer itself states this: " I believe this answer is perfectly appropriate for the question as given the context which I'm inferring is "username, password, email" , they're not checking for 0 values.
Given the popularity of this question and answer, however, I agree that it's worth mentioning in the answer itself. Hendeca - rolls eyes Go read the code in the actual question.
It's clearly asking about usernames and passwords. I'm not guessing at anything, I was just being polite. You're bothered by the fact that I answered what they needed and not what they asked, which is absurd. This is SO, most of the time people don't know what they should be asking for. In the context of the original question this answer is correct. Now stop adding noise. Show 4 more comments. WebWanderer WebWanderer 8, 3 3 gold badges 27 27 silver badges 43 43 bronze badges.
HunanRostomyan Good question, and honestly, no, I do not think that there is. Not very usefull, but I did it anyways. I'm going to do something that is almost never a good idea: change the code in this answer. Specifically, remove the totally unnecessary test for type object, when checking for null. This is a fundamental code snippet: not a good idea to have even a single beginner mis-learn that they need to do that verbose test.
Show 3 more comments. This only works if you consider undefined to be not null. Otherwise it will lead to a lot of unexpected behavior. AndrewMao undefined is not null : stackoverflow. I believe that's what AndrewMao was saying, really. His first sentence might be rewritten "This only works in situations where undefined and null are not practical equivalents.
AndrewMao You are very welcome. And I wouldn't call your writing poor, personally; I'd say it's a good deal better than average. Add a comment.
You can check if some value is null as follows [pass,cpass,email,cemail,user]. In addition to the 2 diagrams above.
Improvement over the accepted answer by explicitly checking for null but with a simplified syntax: if [pass, cpass, email, cemail, user]. A cleaner way to do your check would be to simply use the!
Nikhil Agrawal Joey C. That code is probably in a function, he just didn't show it ; — Nobody. Do not use try and catch for flow of control. This is not a good solution. In JavaScript, no string is equal to null. Michael Laszlo Michael Laszlo Sunny Patel 7, 2 2 gold badges 30 30 silver badges 42 42 bronze badges. Nejmeddine Jammeli Nejmeddine Jammeli 8 8 silver badges 15 15 bronze badges.
Naeem Baghi Naeem Baghi 2 2 gold badges 12 12 silver badges 27 27 bronze badges. I think you meant value! That's actually the same as value! The solution reads as if!
Gabriel Gabriel 4 4 silver badges 14 14 bronze badges. Thanks for pointing out the bug Gabriel, I've put the fix into my answer. Aside from that, I was able to fix the test by changing parseInt to parseFloat which should have been obvious to me in the first place. I avoided using the isNan function because I feel as if many developers view functions such as isNaN as some sort of "magic box" that values go into and booleans come out of, and I wanted to should the test a little more in depth.
A function returns null, or it is allocated to a variable. For example, a function such as greetObject can create objects and return a null. In this case, the function has an argument. But if you would invoke that same function without an argument, then it will return null. For instance, having a greetObject results in a null. As a result, it is impossible to create a greeting object.
In API, null is retrieved in locations where an object is expected, but no object is relevant. JavaScript coerces falsy to false if a falsy value is encountered in conditionals. The typeof operator checks the type of variable in JavaScript. It is a unary operator that returns a string denoting the class of the unassessed operand.
The null value details the intended emptiness of Object. The standard way JavaScript check if value is null is via the equality operators. A good way of checking null in JavaScript is using a strict equality operator. Ideally, if you need absolute checks, implement the use of absolute equals, i. Else, it leads to unexpected conversions occur. So, always use three equals unless you have a compelling reason to use two equals.
Note that null is not loosely equal to falsy values except undefined and null itself. The strict equality operator regards operands of different caliber to be different. X and y are values that produce true or false.
Otherwise, it will return false. Similarly, for not equal to! Else, it will return false. So, if Type x is Null , return true, i. However, it attempts to convert and compare operands that are of different types. If you want to check whether two values are similar, use the JavaScript Object is. However, if you want to check for null values, the Object. The use JavaScript Object. The Object. By now, you know that null appears in positions you would otherwise anticipate an object.
Now, extracting an attribute from null is not a good idea because JavaScript will throw an error. The who function is an empty strict; thus, the function returns null.
When you access the message property, JavaScript throws a TypeError error is thrown. In most cases, developers may be tempted to return null when they cannot construct an object.
It is possible, but the process has negatives. Once you spot null, check for it. If you do not want to return an error, two other things are possible. First, outputting the default object rather than null.
0コメント