Styjun

eval is one option.

var a = 1;
var name = 'a';

document.write(eval(name)); // 1

You can use the window object to get at it .

window['myVar']

window has a reference to all global variables and global functions you are using.

Just don't know what a bad answer gets so many votes. It's quite easy answer but you make it complex.

// If you want to get article_count
// var article_count = 1000;
var type = 'article';
this[type+'_count'] = 1000; // in a function we use "this";
alert(article_count);

a = 'varname';
str = a+' = '+'123';
eval(str)
alert(varname);

Try this...

This is an example :

for(var i=0; i<=3; i++) 
 window['p'+i] = "hello " + i;


alert(p0); // hello 0
alert(p1); // hello 1
alert(p2); // hello 2
alert(p3); // hello 3

Another example :

var myVariable = 'coco';
window[myVariable] = 'riko';

alert(coco); // display : riko

So, the value "coco" of myVariable becomes a variable coco.

Because all the variables in the global scope are properties of the Window object.

In Javascript you can use the fact that all properties are key value pairs. jAndy already mentioned this but I don't think his answer show how it can be exploited.

Usually you are not trying to create a variable to hold a variable name but are trying to generate variable names and then use them. PHP does it with $$var notation but Javascript doesn't need to because property keys are interchangeable with array keys.

var id = "abc";
var mine = ;
mine[id] = 123;
console.log(mine.abc);

gives 123. Usually you want to construct the variable which is why there is the indirection so you can also do it the other way around.

var mine = ;
mine.abc = 123;
console.log(mine["a"+"bc"]);

If you don't want to use a global object like window or global (node), you can try something like this:

var obj = ;
obj['whatever'] = 'There's no need to store even more stuff in a global object.';

console.log(obj['whatever']);

I needed to draw multiple FormData on the fly and object way worked well

var forms = 

Then in my loops whereever i needed to create a form data i used

forms["formdata"+counter]=new FormData();
forms["formdata"+counter].append(var_name, var_value);

2019

TL;DR

• 
  eval operator can run string expression in the context it called and return the value, also variables;


• 
  literal object theoretically can do that [varName], but it blocked by definition.

So I come across this question and everyone here just play around without bringing a real solution. Thanks to @Axel Heider, who was approaching.

The right solution is eval

The almost most forgotten language operator. ( I think the most one is with )

so reserve word operator eval can dynamically run expression in the context it called. and return the result of that expression. we can use that to dynamicly return a value of a variable in a function context.

example:

function exmaple1()
 var a = 1, b = 2, default = 3;
 var name = 'a';
 return eval(name)


example1() // return 1


function example2(option)
 var a = 1, b = 2, defaultValue = 3;

 switch(option)
 case 'a': name = 'a'; break;
 case 'b': name = 'b'; break;
 default: name = 'defaultValue';
 
 return eval (name);


example2('a') // return 1
example2('b') // return 2
example2() // return 3

Note that I always write explicitly the expression eval will run.
To avoid unnecessary surprises in the code. eval is very strong
But I'm sure you know that already

BTW, if it was legal we could use literal object to capture the variable name and value, but we can’t combine computed property names and property value shorthand, sadly, is invalid

functopn example( varName )
 var var1 = 'foo', var2 ='bar'

 var capture = [varName]



example('var1') //trow 'Uncaught SyntaxError: Unexpected token }`

what they mean is no, you can't.
there is no way to get it done.
so it was possible you could do something like this

function create(obj, const)
// where obj is an object and const is a variable name
function const () 

const.prototype.myProperty = property_value;
// .. more prototype

return new const();

having a create function just like the one implemented in ECMAScript 5.

eval() did not work in my tests. But adding new JavaScript code to the DOM tree is possible. So here is a function that adds a new variable:

function createVariable(varName,varContent)

 var scriptStr = "var "+varName+"= ""+varContent+"""

 var node_scriptCode = document.createTextNode( scriptStr )
 var node_script = document.createElement("script");
 node_script.type = "text/javascript"
 node_script.appendChild(node_scriptCode);

 var node_head = document.getElementsByTagName("head")[0]
 node_head.appendChild(node_script);


createVariable("dynamicVar", "some content")
console.log(dynamicVar)

use Object is great too.

var a=123
var b=234
var temp = "a":a,"b":b
console.log(temp["a"],temp["b"]);

Although this have an accepted answer I would like to add an observation:

In ES6 using let doesn't work:

/*this is NOT working*/
let t = "skyBlue",
 m = "gold",
 b = "tomato";

let color = window["b"];
console.log(color);

However using var works

/*this IS working*/
var t = "skyBlue",
 m = "gold",
 b = "tomato";

let color = window["b"];
console.log(color);

I hope this may be useful to some.