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Passing function arguments as parameters in JavaScript

, 6 Aug 2005
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If you're in need of C-like input/output parameters or VB-like "by reference" function arguments in JavaScript, here's some help.

Introduction

When used as function arguments in JavaScript, number and string objects are compared by value, and functions are compared by reference... array objects (arrays) seem to be the only option for passing arguments by reference, so we'll simply wrap an array of size 1 into a new object class that sets/gets the first element:

function param()
{
    this.array = new Array(1);

    this.setValue = function(v) { this.array[0] = v; }
    this.getValue = function()  { return this.array[0]; }
}

It's a simple object with a 1-element internal array that will hold anything (even an object reference), exposing two simple assignment and retrieval methods.

You would typically use it in situations where you need more than one return value.

// declare a variable as a parameter
var s = new param;

// issue a function call using the parameter
var o = output(dText.innerHTML, s, 'Hello, world.');

// the function is obviously designed to treat the 2nd argument as a parameter...
function output(arg1, arg2, arg3)
{
  ...
  // ...so that eventually it can assign a value to it.
  arg2.setValue(a + b % 10);
  ...
}

// when ready to retrieve the output value, use the retrieval function.
dResult.innerHTML += s.getValue() + ' (' + o + ')';

And that's it. You can declare and pass-in as many parameters as you like, as long as your code handles them through the member functions; you can also use the internal array property if you need to handle the argument as an array, say to concatenate with other arrays, etc.

Why not use a one-sized array directly? Good, valid question. Actually, I just wanted to improve the code's readability, and this looked better than handling the 0th element around in functions. Maybe it's a waste of time, but hey, I'm into the "slow down" way of things now.

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About the Author

hector [.j.] rivas
Software Developer (Senior) CompuCom, Inc.
United States United States
Hector J. Rivas has 25+ years of experience managing hardware and software development under many different operating systems, platforms and languages. He has developed microcontroller interfaces and PC games; authored computer based training lessons and delivered fully functional financial and administrative data-intensive applications, as well as image processing and other calculation-intensive applications. Mr. Rivas has also managed Y2K remediation, large scale platform migration and Web site projects, from R&D to actual deployment.
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Comments and Discussions

 
GeneralAwful PinsussAnonymous10-Aug-05 6:27 
GeneralRe: Awful PinmemberTor2k10-Aug-05 6:37 
GeneralRe: Awful PinmemberSebastian Streiger14-Nov-05 8:51 

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