Filling a bi-dimensional array in JavaScript using a for loop

Question

So, I need to fill a bi-dimensional array in JavaScript and I'm doing it the following way:

var i = 0, j = 0;
for (i = 0; i < roomWidth / tileWidth; i += 1) {
     roomBuffer[i] = [];
}
for (i = 0; roomWidth / tileWidth; i += 1) {
     for (j = 0; j < roomHeight / tileHeight; j += 1) {
          roomBuffer[i][j] = 1;
     }
}
alert("Hello world");

The problem is that it not only doesn't work but any code that comes after it, it's not executed. In this case the alert("Hello world");. What am I doing wrong guys?

If your script stops executing then your browser should log an error in its console. Hopefully that could give you a clue as to what's going on; it's hard for us to know without the full code, for example what is the roomWidth variable? — lpd
– lpd, Commented Feb 4, 2012 at 0:28
Thanks everyone for your answers! I should have checked the javascript console before asking here though — federicot
– federicot, Commented Feb 4, 2012 at 1:47

Yuriy Zubarev · Accepted Answer · 2012-02-04 00:27:20Z

4

change

for (i = 0; roomWidth / tileWidth; i += 1) {

to

for (i = 0; i < roomWidth / tileWidth; i += 1) {

answered Feb 4, 2012 at 0:27

Yuriy Zubarev

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Comments

chharvey · Accepted Answer · 2012-02-04 00:43:36Z

1

You don't need to declare i and j before the loops. If their existence is solely for the loops, they are better off as local variables. Also, you can combine loops.

Also, what @Yuriy Zubarev said is right. The middle statement in the for-loop is a condition that must hold true throughout the loop.

for (var i = 0; i < roomWidth / tileWidth; i++) {
     roomBuffer[i] = [];
     for (var j = 0; j < roomHeight / tileHeight; j++) {
          roomBuffer[i][j] = 1;
     }
}
alert("Hello world");

edited Feb 4, 2012 at 0:43

answered Feb 4, 2012 at 0:29

chharvey

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4 Comments

david Over a year ago

You're misunderstanding javascript's scoping rules. i and j will not be discarded after the loops.

david Over a year ago

Don't call them local variables :S and it's not good to declare them inside the for loop. The general consensus is manually hoisting variable declarations to the top of the containing function is best.

chharvey Over a year ago

@david really?? I'm new to JavaScript but I've been coding in Java for years (ok, so only 3 years) but I was always taught that it's best to declare the loop counter inside the loop definition...

david Over a year ago

That's because Java is block scoped, javascript is function scoped. If you declare them inside the loop definition you're just lying to yourself.

hrishikeshp19 · Accepted Answer · 2012-02-04 00:48:03Z

1

Have a look at this fiddle.

change your

for (i = 0; roomWidth / tileWidth; i += 1)

to

for (i = 0; i < roomWidth / tileWidth; i += 1)

answered Feb 4, 2012 at 0:48

hrishikeshp19

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Comments

georg · Accepted Answer · 2012-02-04 00:54:31Z

0

You can simplify your code by using a small helper function

// create an array of length len filled with value
fill = function(len, value) {
    for (var a = []; len-- > 0; a.push(value));
    return a;
}

Your code:

size = roomWidth / tileWidth
roomBuffer = fill(size, fill(size, 1))

answered Feb 4, 2012 at 0:54

georg

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