How to check 'undefined' value in jQuery
JQuery library was developed specifically to simplify and to unify certain JavaScript functionality.
However if you need to check a variable against undefined
value, there is no need to invent any special method, since JavaScript has a typeof
operator, which is simple, fast and cross-platform:
if (typeof value === "undefined") {
// ...
}
It returns a string indicating the type of the variable or other unevaluated operand. The main advantage of this method, compared to if (value === undefined) { ... }
, is that typeof
will never raise an exception in case if variable value
does not exist.
In this case you can use a === undefined
comparison: if(val === undefined)
This works because val
always exists (it's a function argument).
If you wanted to test an arbitrary variable that is not an argument, i.e. might not be defined at all, you'd have to use if(typeof val === 'undefined')
to avoid an exception in case val
didn't exist.