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

Posted by jpluimers on 2017/10/11

Yes there is; it’s the answer below. Note I needed to exclude false by adding a check value === false to the code below as that was a valid value for me.

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 truthyvalue like shown above.

Further read: http://typeofnan.blogspot.com/2011/01/typeof-is-fast.html

Thanks to [WayBackUser jAndy – Stack Overflow who answered the above at [WayBackIs there a standard function to check for null, undefined, or blank variables in JavaScript? – Stack Overflow.

–jeroen

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