Last Updated: February 25, 2016

JavaScript function overloading

This is an example of function overloading in JavaScript

http://ejohn.org/blog/javascript-method-overloading/

function _add(object, name, fn){
    var old = object[ name ];
    if ( old )
        object[ name ] = function(){
            if ( fn.length == arguments.length )
                return fn.apply( this, arguments );
            else if ( typeof old == 'function' )
                return old.apply( this, arguments );
        };
    else
        object[ name ] = fn;
}

Now use the function overloading

function Users(){}
_add(Users.prototype, "find", function(){
  // Find all users...
});
_add(Users.prototype, "find", function(name){
  // Find a user by name
});
_add(Users.prototype, "find", function(first, last){
  // Find a user by first and last name
});

var users = new Users();
users.find(); // Finds all
users.find("John"); // Finds users by name

#function

#javascript

#overloading

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2 Responses

Add your response

steve-jansen

For me, this technique is harder to read over putting the logic to inpsect the arguments array inside your object's function, and then make decisions on the logic to apply. I might use a closure like this:

(function(){
 function findAll() {
   // Find all users...
  }

 function findByFullName(name) {
  // Find a user by name
  }

  function findBySurname(first, last) {
     // Find a user by first and last name
  }

  Users.prototype.find = function find() {
    if (arguments.length === 0)
       return findAll.apply(this);

    if (arguments.length === 1 and typeof(arguments[1]) === 'string')
      return findByFullName.apply(this, arguments);

   // by default, search using first and last name
   return findBySurname.apply(this, arguments);
  }
})();

over 1 year ago ·

stevenanavay

Thanks Steve,
I think your version is really nice. I am going to give it a try and might change to this approach in the future.

over 1 year ago ·