Dynamic variable in loop javascript

Question

I want to create a dynamic variable in the loop. I found something about eval and window but I don't know how to use this.

This is my loop and i want to create a 9 variables names from m1 to m9. I mean that the name of variable must be m1 to m9

for(i=1; i<10; i++){

  var m+i = "Something"

}

Please help me with this. Really appreciate.

http://stackoverflow.com/questions/13291554/dynamic-variables-names-in-javascript — gongzhitaao, May 22 '14 at 13:52
Why would you do this rather than simply using existing array or object syntax? — Jason M. Batchelor, May 22 '14 at 13:52
Yes, you can indeed do this with `eval`. But *should* you do it? It's almost *always* better to use an array and use `m[0]` to `m[8]`. — Mattias Buelens, May 22 '14 at 13:53

score 4 · Accepted Answer · edited May 22 '14 at 13:54

4

You don't want to create 9 variables. Trust me. You want to create an object.

var m = {};
for(var i=1; i<10; i++){
    m[i] = "Something";
}

You can also create an array (m = []), but since you are starting at 1 and not 0, I'd suggest an object.

edited May 22 '14 at 13:54

Mattias Buelens

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answered May 22 '14 at 13:52

gen_Eric

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I would go for the array as it has numbered indices ! – adeneo May 22 '14 at 13:54
1

If the OP doesn't need to start at 1 (for some reason) then, I'd agree @adeneo, but Rocket's solution already states the reasoning for using an object is tied to the OP's code stating it starts at 1. Of course, it'd also be easier to advise the OP if they could explain /why/ they felt the need to have dynamic ordered variables in the first place. – Jason M. Batchelor May 22 '14 at 13:56
@adeneo: I originally had the answer with an array, but I changed to an object, because in this case `m[0]` would be unset, and I was unsure if that would be a problem here. What if his `i` started at `10` or `100`? That is why I used an object. – gen_Eric May 22 '14 at 13:59
@MattiasBuelens: Thanks for editing the post. I copied and pasted the OP's code, so I forgot to fix the `var` :-) – gen_Eric May 22 '14 at 14:00

score 2 · Answer 2 · answered May 22 '14 at 13:55

2

But if you still want to create 9 variables, despite all that, you still can:

for(i=1; i<10; i++){
  eval('var m'+i+'='+i)
}

(And yes, you shouldn't).

answered May 22 '14 at 13:55

punund

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This is true. You *can* do it, but it's not suggested :-) – gen_Eric May 22 '14 at 14:00

score 1 · Answer 3 · edited May 22 '14 at 14:08

1

var object = {};     
var name = "m";
for(i=1; i<10; i++){
  object[name+i] = "Something";
}
console.log(object.m1); // "Something", same for m2,m3,m4,m5...,m9

However consider if the "m" is really necessary, arrays are way faster:

var array = [];
for(i=1; i<10; i++){
  array.push("Something");
}
console.log(array[0]); // "Something", same for 1,2,...,8

edited May 22 '14 at 14:08

punund

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answered May 22 '14 at 13:55

Tomáš Zato

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Dynamic variable in loop javascript

3 Answers3