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up vote 2 down vote favorite

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?

share|improve this question
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 Feb 4 '12 at 0:28
where are you declaring roombuffer? – hrishikeshp19 Feb 4 '12 at 0:31
Thanks everyone for your answers! I should have checked the javascript console before asking here though – John Doe Feb 4 '12 at 1:47

4 Answers

up vote 4 down vote accepted

change

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

to

for (i = 0; i < roomWidth / tileWidth; i += 1) {
share|improve this answer
up vote 1 down vote

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");
share|improve this answer
You're misunderstanding javascript's scoping rules. i and j will not be discarded after the loops. – david Feb 4 '12 at 0:33
sorry. fixed my answer. – TestSubject528491 Feb 4 '12 at 0:43
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. – david Feb 4 '12 at 0:46
@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... – TestSubject528491 Feb 4 '12 at 1:01
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. – david Feb 4 '12 at 1:38
up vote 1 down vote

Have a look at this fiddle.

change your

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

to

for (i = 0; i < roomWidth / tileWidth; i += 1)
share|improve this answer
up vote 0 down vote

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))
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