From Egist Li

Avoid ReferenceError in Javascript

As mentioned in the previous post, a reference comprises two parts: base value and reference name, for example: in the reference “window.console”, “window” is the base value and “console” is the reference name. The ReferenceError is raised when the base value of a reference could not been resolved. The easiest way to check variables is using typeof:

if(typeof undefinedVar === ‘undefined’) {}

It works across all situations without raising ReferenceError, but writing this kind of checks is really tedious.

So, how can we avoid ReferenceError without typing “typeof …” all the time?

To sum it up, just check global object properties like below no matter where the code is (global scope or function scope):

if(window.console) {

    // do something with console object

}

Any other variables such as function arguments or local variables in the function scopes, check them like this:

(function(window, undefined){

    var foo = aFunctionMayReturnUndefined();

    if(foo) {

        //do something with foo

    }

    if(window.console) {

    }

})(window)

The only requirement of this defined checking is declaring local variables in your function correctly.