The JavaScript Global Object

The global object is an object that is initialised by the JavaScript interpreter before the code is executed. All variables that are declared on the global scope (see: Scopes) are stored in the global object as properties.

In a Node.js environment, the global object can be accessed by the global keyword, while in a browser window it can be accessed by the window keyword. The this keyword also refers to the global object when used in the global scope. Please note that using this in the global scope will return undefined if strict mode is enabled.

For example:

// global scope
var foo = "bar";

console.log(global.foo); // bar (in a Node environment)
console.log(window.foo); // bar (in a browser window)
console.log(this.foo); // bar (if strict mode is disabled)

The distinction between scopes local to functions and the global scope is important here: the global object only contains the variables that were declared on the global scope, not the local scopes of functions.

The global object also contains the properties NaN, undefined and Infinity and the following functions:

1. decodeURI()
2. decodeURIComponent()
3. encodeURI()
4. encodeURIComponent()
5. escape()
6. eval()
7. GetObject()
8. isFinite()
9. isNaN()
10. parseFloat()
11. parseInt()
12. ScriptEngine()
13. ScriptEngineBuildVersion()
14. ScriptEngineMajorVersion()
15. ScriptEngineMinorVersion()
16. unescape()

References

1. MSDN: Global Object (Javascript)