Is there a better way to do optional function parameters in JavaScript?

javascript function arguments
Mark Biek picture Mark Biek · Sep 29, 2008 · Viewed 415k times · Source

I've always handled optional parameters in JavaScript like this:

function myFunc(requiredArg, optionalArg){
  optionalArg = optionalArg || 'defaultValue';

  // Do stuff
}

Is there a better way to do it?

Are there any cases where using || like that is going to fail?

Answer

Paul Dixon picture Paul Dixon · Sep 29, 2008

Your logic fails if optionalArg is passed, but evaluates as false - try this as an alternative

if (typeof optionalArg === 'undefined') { optionalArg = 'default'; }

Or an alternative idiom:

optionalArg = (typeof optionalArg === 'undefined') ? 'default' : optionalArg;

Use whichever idiom communicates the intent best to you!

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