JavaScript function optional parameter | 3 Ways Examples code

You can declare a function with optional parameter using Logical OR operator (‘||’) or Assignment operator (“=”), etc in JavaScript.

JavaScript function optional parameter can do it in 3 ways:-

  • Undefined property
  • OR (||) operator
  • The assignment operator (“=”)

Declare optional function parameters in JavaScript Example

Let’s see all method examples in HTML:-

Using undefined property

Undefined property indicates that a value is not assigned to a variable.


JavaScript function optional parameter Undefined

OR (||) operator

In the example the optional parameter is ‘b’:

The optional parameter is Logically OR with the default value within the body of the function and should always come at the end of the parameter list.

Pre ES2015,


JavaScript function optional parameter OR operator

The assignment operator (“=”)

The optional variable is assigned the default value in the declaration statement itself and should end on the parameter list.

From ES6/ES2015, default parameters are in the language specification.


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Do comment if you have any doubts and suggestion on this JS function topic.

Note: All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version

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