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Method overloading in Javascript March 11, 2008

Filed under: ajax,javascript — nagoon97 @ 4:51 pm
Tags: , , ,

To simulate method overloading in Javascript, many “if” statements are often used, which makes the code alot less intuitive.

So, I came up with the following function to simulate method overloading without harming the readability of the source code.

/**
 * You can find more about this function at
 * http://nagoon97.com/method-overloading-in-javascript/
 *
 * Copyright (c) 2008 Andy G.P. Na <nagoon97@gmail.com>
 * The source code is freely distributable under the terms of an MIT-style license.
 */
function methodOverloading(funcName, args){
  var sFuncName = funcName;
  var func = null;

  sFuncName += "$"+getType(args[0]);
  for(var i=1; i<args.length; i++){
    sFuncName += "$"+getType(args[i]);
  }

  if(func = eval(sFuncName))
    return func.apply(this, args);

  throw(sFuncName+" is not defined");
}

Just place the function like the following and you are ready to go.

function add(){
  // pass in the function name as the 1st element of the 2nd argument
  return methodOverloading.apply(this, ["add", arguments]);
}

Now, you can overload a function just by naming the new functions with the type of parameters that the function takes, each parameters separated by a string.

function add$string$string(str1, str2){
  return str1 + ", " + str2;
}

function add$number$number(num1, num2){
  return num1 + num2;
}

function add$undefined(){
  return "no parameter is given!";
}

And when you call the function

alert(add("s1", "s2")); // this will display "s1, s2"
alert(add(1, 2)); // this will display 3
alert(add()); // this will display "no parameter is given!"

Please note that you need to include getType() function that I have posted HERE.
getType() is used to give methodOverloading() function the ability to overload method with user defined custom objects.
If this feature is not needed and you do not want to include the function, you can change it to typeof() and use it as

function methodOverloading(funcName, args){
  var sFuncName = funcName;
  var func = null;

  sFuncName += "$"+typeof(args[0]);
  for(var i=1; i<args.length; i++){
    sFuncName += "$"+typeof(args[i]);
  }

  if(func = eval(sFuncName))
    return func.apply(this, args);

  throw(sFuncName+" is not defined");
}

And just in case you were wondering how to use this in a function,

function inc(){
 this.do = function(){
  return methodOverloading.apply(this, ["this.do", arguments]);
 }
 this.do$string = function(str){
  return str+", "+str;
 }
 this.do$number = function(num){
  return num+1;
 }
}

oInc = new inc();

alert(oInc.do("ABC"));
alert(oInc.do(1));
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3 Responses to “Method overloading in Javascript”

  1. Good stuff, but last I checked, typeof is an operator and not a function, so in the alternate version, it’ll be

    typeof args[0]

    instead of

    typeof(args[0])

  2. nagoon97 Says:

    Hello Jaffer ^-^
    Yes, you are right, typeof is an operator but placing parentheses around the operand is allowed and I think it makes the source code easier to read because the operator looks alot like a name of an instance without the parentheses.

    alert(type1 + typeof(type2) + type3);
    alert(type1 + typeof type2 + type3);

  3. cool, didn’t know that.


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