Value of null in javascript

If you try to find DOM element using document. So it is recommended to check for null before doing something with that element. A null value evaluates to false in conditional expression. Undefined is also a primitive value in JavaScript.

A variable or an object has an undefined value when no value is assigned before using it. So you can say that undefined means lack of value or unknown value. In the above example, we have not assigned any value to a variable named 'myVar'. A variable 'myVar' lacks a value. So it is undefined. You will get undefined value when you call a non-existent property or method of an object. In the above example, a function Sum does not return any result but still we try to assign its resulted value to a variable.

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.

But yes, your suggested test will work and is perfectly fine to use. Sorry I didn't notice your post until now. Great, that seems to work. Thanks for the comment on why you avoided isNaN as well, I can get behind that logic. There's also the Underscore. Mark Rotteveel ToolmakerSteve 9, 10 10 gold badges 74 74 silver badges bronze badges. Kaleem Ullah Kaleem Ullah 5, 2 2 gold badges 38 38 silver badges 44 44 bronze badges. This answer has nothing to do with this post.

Did you post this answer on this thread by accident? This isEmpty function behaves exactly like! No need to invent a function. Just do if! Which is already shown in the accepted answer. And per WebWanderer's comment, the middle part of this post, "try-catch exceptional API call", does not appear to be relevant to this question. Please explain your intent - when is that useful? How does that relate to the question? Tarmo Saluste Tarmo Saluste 5 5 silver badges 17 17 bronze badges.

But it could be a very large object that we haven't even made. Neithan Max Neithan Max 8, 4 4 gold badges 34 34 silver badges 54 54 bronze badges. Try this: if! THX Also someone already provided that answer last year: stackoverflow.

Codiee Codiee 2, 2 2 gold badges 14 14 silver badges 17 17 bronze badges. P-S P-S 3, 24 24 silver badges 25 25 bronze badges. What about optional check with operator? Pit Pit 10 10 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Objects are complex data structures. The simplest object in JavaScript is the plain object — a collection of keys and associated values:. But there are situations when an object cannot be created.

For such cases, JavaScript provides a special value null — which indicates a missing object. In this post, you'll learn everything about null in JavaScript: its meaning, how to detect it, the difference between null and undefined , and why using null extensively creates code maintenance difficulties.

The JavaScript specification says about null :. If you see null either assigned to a variable or returned by a function , then at that place should have been an object, but for some reason, an object wasn't created. For example, the function greetObject creates objects, but also can return null when an object cannot be created:. However, when invoking the function with no arguments — greetObject — the function returns null.

Returning null is reasonable because who parameter has no value, and the greeting object cannot be created. Thinking about a real-world analogy, you can imagine a variable as being a box. Just like a variable can hold an object, the box can contain objects like a teapot. But once you receive a box and open it Someone made a mistake and sent you an empty box. The box contains nothing, or, saying it differently, contains a null value. The good way to check for null is by using the strict equality operator :.

If a falsy value is encountered in conditionals, then JavaScript coerces falsy to false.