How can I define an array with variables and then populate each with a number?

Question

I have an array with multiple variables defined in it. But when trying to set each of them to 0 I get an error that states the first variable of the array is undefined.

Here is what I have:

var keys = [key1, key2, key3, etc...];

function loadKeys(){
    for(i=0;i<36;i++) {
        keys[i] = 0;
    }
}

What is `key1`, `key2`, etc.? If they are variables and you have not defined them previously, they will be `undefined`. So your array will look like `[undefined, undefined, ..., undefined]`. — Vivin Paliath, Jan 20 '15 at 16:09
So, I have to define each variable in the array beforehand? I have 35 of them... — wahle509, Jan 20 '15 at 16:10
It's not clear what you're trying to accomplish. Are you trying to initialize an array with some pre-defined values? — Vivin Paliath, Jan 20 '15 at 16:11
@wahle509: No, you just should not use them if you actually don't need them? — Bergi, Jan 20 '15 at 16:11
@VivinPaliath they are "not defined", as opposed to `undefined`. Trying to access them will cause a `ReferenceError`. — joews, Jan 20 '15 at 16:35

score 2 · Answer 1 · answered Jan 20 '15 at 16:19

The error is being cause because key1 is undefined as a variable. There are actually several different ways you could do this, including manually setting the keys.

var keys = [0,0,0,0...]

instead of typing all this out however if your keys have a default value you could always initialize the array with a push command

var keys = [];
for (int i= 0; i<36;i++){
    keys.push({defaultValue});
}

that will make all the elements in you array defined with a default value rather than as an undefined element

score 2 · Answer 2 · edited May 23 '17 at 12:22

Your code fails with a ReferenceError because key1, key2 etc don't exist - the JavaScript runtime doesn't know what value you are asking for.

Your example doesn't actually need these variables to be set. If you simply want an Array of 35 elements, all set to 0, you can use:

var keys = [];
for(var i = 0; i < 36; i ++) {
  keys.push(0);
}

For other ways to do this, see Most efficient way to create a zero filled JavaScript array?

Looking a small distance into the future, ES6 provides Array.prototype.fill:

var keys = new Array(35);
keys.fill(0);

This method is not widely implemented yet, but you can try it out in Firefox 31+.

ES6 compatibility table

score 0 · Answer 3 · answered Jan 20 '15 at 16:13

0

var keys = ['key1', 'key2', 'key3'];

function loadKeys(){
    for(i=0;i<36;i++) {
        keys[i] = 0;
    }
}

is working for me so far. I don't get your issue though, are those variables in your array ?

answered Jan 20 '15 at 16:13

Valentin Roudge

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How can I define an array with variables and then populate each with a number?

3 Answers3