如何检索阴影全局变量的值？

Question

Example:

var test = 'global value';

(function() {
    var test = 'local value';

    // how to get the 'global value' string
})();

Given the condition that the host environment is unknown, meaning that we cannot assume that the global object will be accessible via the window name. Also, the function is not allowed to receive any arguments!

Answer 1

The fix

var test = 'global value';

(function() {
    var test2 = 'local value';

    console.log(test);
})();

The real solution is to fix your code so your not shadowing global variables you care about.

Eval work around

You can always use global eval, it's the most reliable.

Example

var test = 'global value';

function runEval(str) {
  return eval(str);
}

(function() {
    var test = 'local value';

    console.log(runEval("test"));
})();

If you don't like defining a global eval you can use Function to do it indirectly

Live Example

var test = 'global value';

(function() {
    var test = 'local value';

    console.log(new Function ("return test;") () );
})();

Miscellaneous hacks

The following works in non strict mode

(function () {
  var test = "shadowed";

  console.log(this !== undefined && this.test);
})();

And this hack works in broken implementations

(function() {
    var test = 'local value';

    try { delete test; } catch (e) { }

    console.log(test);
})();

Answer 2

What about relying on its this as the global object (no explicit reference to window ).

console.log(this.test);

jsFiddle .

You could also use an indirect call to eval() ( execScript() is here for IE purposes, but feel free to ignore as you mentioned to not assume a browser).

console.log((window.execScript || eval)('test'));

jsFiddle .

Answer 3

Fundamentally the big issue, if you want to do this in strict-mode code, is getting the global object. Thankfully there are some simple ways: var global = (1,eval)("this"); (which doesn't work in every browser, as its behaviour is undefined in ES3, though defined in ES5) or var global = (new Function("return this"))(); (which does).

So, put that together with what else you need, you can have a function such as:

function getGlobal(name) {
  "use strict";
  var global = (new Function("return this"))();
  return global[name];
}

It'd probably be better to avoid the cost of creating a function each time, so something like the following would be better:

var getGlobal = (function() {
  "use strict";
  var global = (new Function("return this"))();
  return function(name) {
    return global[name];
  }
})();

Answer 4

There is globalThis since ES2020, supported by all modern browsers.

var test = 'global value';

(function() {
    var test = 'local value';

    console.log(globalThis.test); // 'global value'
})();

Answer 5

It depends. A "cheeky" way to get past the "not allowed to receive any arguments" might be to use call :

var test = 'global value';

(function() {
    var test = 'local value';

    var globalTest = this.test;
}).call(this);

But if you can count on this being the global object when no this is explicitly specified, then this.test will work.

Answer 6

Another solution is to memoize the global object:

var test = "global";
function called() {
    var test = "local";
    alert(arguments.callee.window.test); // alerts "global"
}
called.window = this;
called();