Question

I’ve seen tons of posts about the difference between global and function scope in JavaScript, far too many to link here. I’ve also seen my exact question asked about Python. So what I want to know is, how can I access a global variable when a “closer” scope also has a variable with the same name?

var a = "global";
function b(){
  var a = "local";
  var magic = ...; // somehow put "global" in magic
  console.log(magic); // should print "global"
}

In browser only, I figured out that you can use window.a to specify the global. Is there anything that works server-side as well?

Answer 1

If it’s really a global (i.e. not just in the outer scope), you can do this :

var magic = (function(name){return this[name]}).call(null, "a");

From ECMAScript’s documentation (10.4.3) :

Entering Function Code

The following steps are performed when control enters the execution
context for function code contained in function object F, a caller
provided thisArg, and a caller provided argumentsList:

If the function code is strict code, set the ThisBinding to thisArg.
Else if thisArg is null or undefined, set the ThisBinding to the
global object.

Note that you can’t test this in jsFiddle, as the global scope isn’t where you define your a.

Demonstration:

var a = "global";

function b(){
  var a = "local";
  var magic = (function(name){return this[name]}).call(null, "a");
  document.body.textContent = 'a: '+JSON.stringify(magic); // print "global"
}

b();