Declare variable name dynamically in javascript

Question

In JavaScript I want to make a function which takes an argument and in this function a variable will be created whose name will be the value of the argument.
For example if user pass "jack" in the argument then in function I want a variable whose name is jack like:

var jack = "";

• Adrien Lacroix: Why ? What do you want to do next ?
• Ja͢ck: Could you explain the use-case?
• Felix Kling: possible duplicate of "Variable" Variables in Javascript?
• techfoobar: You want this variable defined in the what scope?

Answer 1

Typically, you won't need to do this. As Bergi pointed out, a local variable would usually suffice. However, in the event that you do need to use this technique, you could give the property to the window object:

function setVariable(userPassedString);
 window[userPassedString] = "";
}

Don't use eval for this, ever, no matter how tempted you are to.

• Bergi: And dont use the global object for this, ever, no matter how tempted you are :-)
• Elliot Bonneville: Do you have another solution, Bergi?
• Ja͢ck: Tbh, window isn't that much better.
• Bergi: @Elliot: It depends on the exact use case (which OP did not give), but usually a local object will suffice.
• Elliot Bonneville: Why the downvote? Is there another, better method? @Bergi, I don't know enough to tell the OP what he should and shouldn't do, so I'm just telling him how to do what he asked.

Answer 2

Creating local variables via a function is typically a bad idea. You could accomplish something similar by passing a local object around, e.g.

function setVar(o, name, value)
{
 o[name] = value;
}

Then, inside your local scope:

var o = {};
setVar(o, 'jack', 123);
// o.jack contains 123

In this way, if the need would really arise (this is rarely required) to introduce global variables in this manner, you can always call the function like this:

setVar(window, 'jack', 123);
// now window.jack == jack == 123

Answer 3

The best that you can do about is to create an object and assigns the variable name to the keys of the created object like this -

var myvar={};
function create(var){
 myvar[var]='values';
}

Answer 4

You could always use a dictionary. Here is a very simple stub:

function Dictionary(){
 var container = {};
 this.set = function(key, value){
 container[key] = value;
 }
 this.get = function(key){
 return container[key];
 }
}
var vars = new Dictionary();
vars.set('foo', 'foo rocks');
vars.set('bar', 'bar rocks too');
console.log(vars.get('foo'));
console.log(vars.get('bar'));

Answer 5

To prevent using the window global array, you can create a local array which holds your variables.

function doSomething(var) {
 var vars = {};
 vars[var] = value;
}

• A. Wolff: vars = array(); 'vars' is set on global scope
• Ja͢ck: This is not valid JavaScript.