Personally, I always use the following:
var x;
if( x === undefined) {
//Do something here
}
else {
//Do something else here
}
The window.undefined property is non-writable in all modern browsers (JavaScript 1.8.5 or later). From Mozilla's documentation: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined, I see this: One reason to use typeof() is that it does not throw an error if the variable has not been defined.
I prefer to have the approach of using
x === undefined
because it fails and blows up in my face rather than silently passing/failing if x has not been declared before. This alerts me that x is not declared. I believe all variables used in JavaScript should be declared.
