Understanding function parameters

Question

This probably has been asked before but all I can find are questions regarding C and Bash etc.

Basically I'm having a really hard time getting my head around function parameters and what they reference.

I know that you usually set paramters when you call the function e.g. doSomething(3,'Hello') etc, but when I read code from tutorials like so;

window.onload = initAll;

function initAll() {
    if (document.getElementById) {
        for (var i=0; i<24; i++) {
            setSquare(i);
        }
    }
    else {
        alert("Sorry, your browser doesn't support this script");
    }
}

function setSquare(thisSquare) {
    var currSquare = "square" + thisSquare;
    var colPlace = new Array(0,0,0,0,0,1,1,1,1,1,2,2,2,2,3,3,3,3,3,4,4,4,4,4);
    var colBasis = colPlace[thisSquare] * 15;
    var newNum = colBasis + getNewNum() + 1;

    document.getElementById(currSquare).innerHTML = newNum;
}

function getNewNum() {
    return Math.floor(Math.random() * 15);
}

Where is setSquare() getting the parameter of thisSquare from?

Are you referring to the call setSquare(i)? I'm not entirely sure what your question is. — Greg Hewgill
– Greg Hewgill, Commented Jan 9, 2012 at 22:20

Jemaclus · Accepted Answer · 2012-01-09 22:22:32Z

1

In your first function initAll(), you are calling setSquare(i). In this case, the i is the parameter. According to initAll(), i is a number in the for loop. Essentially what's happening is you're calling setSquare for each square number 0 to 24.

The setSquare() function has renamed the i to thisSquare. Now anywhere inside the setSquare() function, thisSquare is set to the same value that i had before.

Hope that helps, good luck.

answered Jan 9, 2012 at 22:22

Jemaclus

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4 Comments

PI. Over a year ago

Pretty much perfect .... I love clear answers ... bravo ..... Just one more question if you don't mind with regards to setSquare(i), is that basically calling the function before the function has been created?

Peter-Paul van Gemerden Over a year ago

@17bc17: no, JavaScript interpreters "hoist" named function definitions to the top of the scope. So before actually running the code, the interpreter translates it into something like this: pastie.org/3157006

PI. Over a year ago

@PPvg - Thanks for the reply, its much appreciated. Do you have any links which explain this in more detail?, just I'm pretty new to this.

Peter-Paul van Gemerden Over a year ago

@17bc17: This question on SO is a pretty interesting read. Or MDN, of course: MDN: Hoisting and MDN: Functions and function scope.

Brandon · Accepted Answer · 2012-01-09 22:21:40Z

1

Inside of initAll there is the following code:

for (var i=0; i<24; i++) {
   setSquare(i);
 }

So initAll is calling setSquare 24 times. Each time passing in the value of i. (0, 1, 2, etc.). So the value of i is thisSquare

answered Jan 9, 2012 at 22:21

Brandon

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Comments

Pat · Accepted Answer · 2012-01-09 22:22:59Z

0

setSquare is being called in the initAll function, which passes it a value, from 0 to 23. The initAll function is called when the page is loaded (in theory).

answered Jan 9, 2012 at 22:22

Pat

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Arturo Martinez · Accepted Answer · 2012-01-09 22:25:13Z

0

It is getting it from the for loop in the initAll() function in this case, but it could get it from wherever you call setSquare function

answered Jan 9, 2012 at 22:25

Arturo Martinez

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Kris Krause · Accepted Answer · 2012-01-09 22:25:14Z

0

Where is setSquare getting the parameter of thisSquare from?

Right here: setSquare(i);

Inside the setSquare function currSquare ends up being the id of a Dom element (for example, currSquare1).

answered Jan 9, 2012 at 22:25

Kris Krause

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