Null not null in javascript

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.

So in this case, result will be undefined. You should be using the strict not equals comparison operator! It is possibly because the value of val is actually the string "null" rather than the value null. 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 11 years, 10 months ago. Active 1 year, 7 months ago. Viewed k times. YOU what is CW? Add a comment. Active Oldest Votes.

It is really the equivalent of if val , which is much clearer to read. I would stick to that fyi Ujwal,!! Boolean val — thedjaney. I still like the way it looks though! It's not a simple double negative. It's a transforming double negative. You are basically transforming the variable to a boolean. There's a lot to say on the subject but suffice it to say that in cases where your variable is 0 , false , null , undefined or some such value that resolves to true with one!

It should be used sparingly if at all. Show 3 more comments. Strict Not Version if val! Please use ide. Load Comments. What's New. Most popular in JavaScript. How to get selected value in dropdown list using JavaScript? Difference between var, let and const keywords in JavaScript. Most visited in Web Technologies. Installation of Node.

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