Javascript : generate variable by for loop

Question

Am I able to use for loop to declare variables? Because declaring variables with similar one by one is not smart.

For example if I want variables like: DATA1, DATA2 and DATA3, I will normally declare it like below:

var data1 = "";

var data2 = "";

var data3 = "";

And the below is what I expect we can do in the actual code.

Using for loop and using "i" to assign number for each variable.

for(var i = 0; i < 3 ;i++){

    var data+i = "";

}

am I able to do that? I suppose the above code is not the correct way to do that but just a concept.

You should never generate variables that way. Especially when there's that sweet data structure called an array. — Denys Séguret
– Denys Séguret, Commented Aug 17, 2016 at 7:56
so how should i do this with array ? because i cannot predict how many datax i want to have — Anson Aştepta
– Anson Aştepta, Commented Aug 17, 2016 at 7:57
var data=[]; will give you millions of data[x] - read the documentation — mplungjan
– mplungjan, Commented Aug 17, 2016 at 7:57
Arrays don't have a fixed size in JavaScript. You can even build sparse arrays like var arr=[]; arr[55555]=""; — Denys Séguret
– Denys Séguret, Commented Aug 17, 2016 at 7:58
This is a frequent question but it's hard to find a correct QA for closing among the thousands of similar ones having so bad answers. Every time it's answered by new coders in a bad way... — Denys Séguret
– Denys Séguret, Commented Aug 17, 2016 at 8:01

mplungjan · Accepted Answer · 2016-08-17 08:16:53Z

2

You can define Object or Global variable.

var variables = {};

for (var i = 0; i < 3; i++) {

  variables['data' + i] = i;

}

console.log(variables);

// you can use it like variables.data0


// by the way you can define global variables as you want
// but note that this pollutes the global space

for (var i = 0; i < 3; i++) {
  window['data' + i] = i;
}
// so you can use it like

console.log(window.data0, ' or ', data0)

edited Aug 17, 2016 at 8:16

mplungjan

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answered Aug 17, 2016 at 8:00

0xdw

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3 Comments

Anson Aştepta Over a year ago

can i use for loop to call it?

Anson Aştepta Over a year ago

like variables.data[i]

0xdw Over a year ago

@anson920520. just try it. if it works.. doesn't matter

Stefan Kert · Accepted Answer · 2016-08-17 07:59:44Z

1

Because of the fact that javascript is dynamically typed you can do something like that. JavaScript gives you the possibility of accessing variables through a key.

var baseVariable = {};
for(var i = 0; i < 3; i++){
    baseVariable["data" + i] = "ValueForData" + i;
}

You can than access these variables pretty easy by iterating through the baseVariabel, or if you now the exact amount you can even call it like that:

baseVariable.data1

answered Aug 17, 2016 at 7:59

Stefan Kert

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Comments

Andrew B · Accepted Answer · 2016-08-17 08:16:53Z

-1

You can use eval function to evaluate code from string. For example:

var a = 2; eval('alert(a)');

Take a look at assignment chain. May be is would be suitable.

var a = b = c = d = e = f = g = "";

But this ways is not a good practice. As mentioned in comments for your question better way to use array or object to store data.

answered Aug 17, 2016 at 8:16

Andrew B

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