How do I check if the Javascript global object has been tampered with?

Question

How do I check if the Javascript global object has been tampered with?

I just had this really dumb bug that took 20m to find simply because I forgot the var keyword somewhere. I figured it out, but it just got me thinking...

"Is there an easy way to see if any properties were added to the global object?"

Edit: Sorry, forgot to mention the context is in Node.js.

javascript
node.js

Answer 1

ES5’s strict mode prevents this! Just put a 'use strict' statement at the top of any function or source file:

'use strict';

function foo() {
    var x = 5   // Forgot the comma!
        y = 6;  // Fails in strict mode as an implicit global
}

foo();

Linters should also check for this, and you should use both a linter and strict mode, ideally. I recommend JSHint.