CODEWITHSUNDEEP
javascript
Randomblue
Randomblue

Reputation: 116413

Programmatically setting the name of a variable

Is there a shortcut for writing the following 100 assignments?

variable_1 = 1;
variable_2 = 2;
variable_3 = 3;

...

variable_100 = 100;

I have tried

for(var i = 1; i <= 100; i++) {
    variable_ + i = i;
}

but I get the error message "Invalid left-hand side in assignment". Any ideas?

Upvotes: 17

Views: 8288

Answers (8)

Anthony
Anthony

Reputation: 14309

Assuming you're on a browser you can do:

global[variable] = 'hello'

console.log(variable) -> hello

Upvotes: 0

benekastah
benekastah

Reputation: 5711

Here are a few methods:

Method 1: use eval

Here is the most direct method:

for(var i = 1; i <= 100; i++) {
  eval("var variable_" + i + " = " + i);
}
variable_1; // => 1

Disclaimer for the above method: I don't think this problem is a good candidate for using eval. If you do use eval, you should never allow user input to go into what you are evaling, or you could open your site to security risks. That mistake is the main reason people say eval is evil.

Method 2: use dynamically generated object properties

This is a much, much better way:

// If you want these variables to be global, then use `window` (if you're 
// in a browser) instead of your own object.
var obj = {};
for(var i = 1; i <= 100; i++) {
  obj["variable_" + i] = i;
}
obj.variable_1; // => 1

About the note in the comment about using window to create global variables: I would recommend against this, as it is a quick way to pollute your global scope and step on variables unwittingly.

Method 3: use an array

David suggested using an array. This is another great idea, and, depending on what you are trying to do, may be preferred:

var arr = [];
for(var i = 1; i <= 100; i++) {
  arr.push(i);
}
arr[0]; // => 1

Upvotes: 25

Dennis
Dennis

Reputation: 32608

Use an array:

var variable = [];

for(var i = 1; i <= 100; i++) {
    variable[i] = i;
}

By way of analogy, you'd want to use an array instead of 100 variables for the same reason you'd want

<div class="variable"></div>
<div class="variable"></div>
<div class="variable"></div>
//and so on

instead of

<div id="variable_1"></div>
<div id="variable_2"></div>
<div id="variable_3"></div>
//and so on
<div id="variable_100"></div>

Invalid left-hand side in assignment

This error gets generated because variable_ + i is an expression. The interpreter thinks you are trying to add two variables instead of concatenating a variable name and a string. An expression cannot be on the left-hand side of an assignment operation.

Upvotes: 3

Jivago
Jivago

Reputation: 826

Why not using an array instead like this?

<script language="javascript">
var arrayVar = new Array();

for (var i=0; i<100; i++) {
    arrayVar["variable_" + i] = i;
}
</script>

Upvotes: 3

dheerosaur
dheerosaur

Reputation: 15172

You are better off using an array

var variable = [];
for (var i=1; i <= 100; i++) {
  variable[i] = i;
}

Later, you can access the values using variable[1], variable[2] etc.

Upvotes: 6

Esailija
Esailija

Reputation: 140234

for(var i = 1; i <= 100; i++) {
    window["variable_" + i] = i;
}

alert( variable_50 );

alert( variable_34 );

Upvotes: 2

Pranay Rana
Pranay Rana

Reputation: 176956

If it is like that why not to define array of the objects 

var a = new Array();
for(i=0;i<100;i+=)
 a[i] = i;

Upvotes: 3

Shadow Wizzard
Shadow Wizzard

Reputation: 66398

This will do it:

for(var i = 1; i <= 100; i++) {
    eval("variable_" + i + " = " + i + ";");
}

eval is basically evil, but for such purpose it's OK to use it. (reference)

Live test case.

Upvotes: 7

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