CODEWITHSUNDEEP
javascriptarraysloops
Lewis
Lewis

Reputation: 14866

js - loop through multidimensional array

I'm trying to implement jquery hotkeys in a for loop.

acKey = [
    ["keydown", "alt+d", open],
    ["keydown", "alt+a", close],
    ["keydown", "alt+s", max],
];
for(i=0;i<=acKey.length;i++)
{
    $(document).bind(acKey[i][0], acKey[i][1], acKey[i][2]);
}

However, it turned out error Uncaught TypeError: Cannot read property '0' of undefined. What's wrong with my code?

Upvotes: 0

Views: 88

Answers (2)

cardeol
cardeol

Reputation: 2238

Your problem is your index (out of bounds) when i=acKey.length.

You can use i<acKey.lenght or implement a "for each" iteration to avoid confusion:

acKey = [
    ["keydown", "alt+d", open],
    ["keydown", "alt+a", close],
    ["keydown", "alt+s", max],
];

var sub;
for(i in acKey) {
    sub = acKey[i];
    $(document).bind(sub[0], sub[1], sub[2]);
}

Upvotes: 1

slim
slim

Reputation: 41223

With due credit to @Matt who's comment points it out.

The commonest format for looping through an array is:

 for(var i=0; i<array.length; i++) {
     doSomethingWith(array[i];
 }

Note that's a "less than" operator, not a "less than or equal to" operator.

This loop counts from 0 to array.length - 1, because the second part of the for statement: i < array.length, means "keep repeating for as long as i is less than array.length.

... and that's what you want, because arrays are numbered from 0 to length-1. That is, an array of length 4 is numbered 0,1,2,3.

If you loop while i <= 4, then the loop will execute for 0,1,2,3,4 -- and in Javascript, it will get undefined when it references array[4].

Sometimes you do need "<=" in a for loop, but it's very much the exception. Any time you do use "<=", think about adding a comment to say why.

Upvotes: 4

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