"Variable" variables in JavaScript

Question

I know it's possible in PHP to have "variable" variables. For example,

$x = "variable"; $$x = "Hello, World!"; echo $variable; // Displays "Hello, World!" 

Is it possible to refer to a variable by its name as a string in JavaScript? How would it be done?

Answer 1

tl;dr: Don't use eval!

There is no single solution for this. It is possible to access some global variables dynamically via window, but that doesn't work for variables local to a function. Global variables that do not become a property of window are variables defined with let and const, and classes.

There is almost always a better solution than using variable variables! Instead you should be looking at data structures and choose the right one for your problem.

If you have a fixed set of names, such as

// BAD - DON'T DO THIS!!! var foo = 42; var bar = 21;  var key = 'foo'; console.log(eval(key));

store the those name/values as properties of an object and use bracket notation to look them up dynamically:

// GOOD var obj = {   foo: 42,   bar: 21, };  var key = 'foo'; console.log(obj[key]);

In ES2015+ it's even easier to do this for existing variables using concise property notation:

// GOOD var foo = 42; var bar = 21; var obj = {foo, bar};  var key = 'foo'; console.log(obj[key]);

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If you have "consecutively" numbered variables, such as

// BAD - DON'T DO THIS!!! var foo1 = 'foo'; var foo2 = 'bar'; var foo3 = 'baz';  var index = 1; console.log(eval('foo' + index));

then you should be using an array instead and simply use the index to access the corresponding value:

// GOOD var foos = ['foo', 'bar', 'baz']; var index = 1; console.log(foos[index - 1]);