Is there a standard function to check for null, undefined, or blank variables in JavaScript?

Question

Is there a universal JavaScript function that checks that a variable has a value and ensures that it's not undefined or null? I've got this code, but I'm not sure if it covers all cases:

function isEmpty(val){     return (val === undefined || val == null || val.length <= 0) ? true : false; } 

Answer 1

You can just check if the variable has a truthy value or not. That means

if( value ) { } 

will evaluate to true if value is not:

• null
• undefined
• NaN
• empty string ("")
• 0
• false

The above list represents all possible falsy values in ECMA-/Javascript. Find it in the specification at the ToBoolean section.

Furthermore, if you do not know whether a variable exists (that means, if it was declared) you should check with the typeof operator. For instance

if( typeof foo !== 'undefined' ) {     // foo could get resolved and it's defined } 

If you can be sure that a variable is declared at least, you should directly check if it has a truthy value like shown above.

Answer 2

The verbose method to check if value is undefined or null is:

return value === undefined || value === null; 

You can also use the == operator but this expects one to know all the rules:

return value == null; // also returns true if value is undefined