Update 2019
With all of today's Webpacks and Broccolis, and Gulps and Grunts, and TypeScripts and AltScripts, and create-react-apps, etc, this is pretty useless, but if you're just working with plain, old, VanillaJS and you want to make it isomorphic, this is probably your best option:
var global
try {
global = Function('return this')();
} catch(e) {
global = window;
}
The Function constructor invocation will work even when using --use_strict in node, as the Function constructor always executes in a global non-strict scope.
If the Function constructor fails, it's because you're in a browser with eval disabled by CSP headers.
Of course, with Deno on the way (the node replacement), they may also disallow the Function constructor, in which case it's back to enumerating objects like global, module, exports, globalThis and window, and then duck-type checking which is the global exhaustively... :-/
Crazy one-line solution (Original):
var global = Function('return this')() || (42, eval)('this');
.
.
.
Works
- in every environment (that I tested)
- in strict mode
- and even in a nested scope
Update 2014-Sept-23
This can now fail if HTTP headers in the latest browsers explicitly forbid eval.
A workaround would be to try / catch the original solution as only browsers are known to run this type of subset of JavaScript.
var global;
try {
global = Function('return this')() || (42, eval)('this');
} catch(e) {
global = window;
}
Example:
---
(function () {
var global = Function('return this')() || (42, eval)('this');
console.log(global);
// es3 context is `global`, es5 is `null`
(function () {
"use strict";
var global = Function('return this')() || (42, eval)('this');
console.log(global);
}());
// es3 and es5 context is 'someNewContext'
(function () {
var global = Function('return this')() || (42, eval)('this');
console.log(global);
}).call('someNewContext');
}());
Tested:
---
* Chrome v12
* Node.JS v0.4.9
* Firefox v5
* MSIE 8
Why:
---
In short: it's some weird quirk. See the comments below (or the post above)
In `strict mode` `this` is never the global, but also in `strict mode` `eval` operates in a separate context in which `this` *is* always the global.
In non-strict mode `this` is the current context. If there is no current context, it assumes the global. An anonymous function has no context and hence in non-strict mode assumes the global.
Sub Rant:
There's a silly misfeature of JavaScript that 99.9% of the time just confuses people called the 'comma operator'.
var a = 0, b = 1;
a = 0, 1; // 1
(a = 0), 1; // 1
a = (0, 1); // 1
a = (42, eval); // eval
a('this'); // the global object
