How is this "object expected" JavaScript error possible?

Question

Apparently this line of code is triggering "Object expected":

var bPid = (b != null && typeof (b.processId) == "number") ? b.processId : 0;

Unfortunately I can't step through the code in the debugger since this is an intermittent error that shows up in a Windows SideShow gadget that I'm writing. But, I'd imagine someone should be able to tell me how it's even possible to get object expected given all the checks that I'm doing to attempt to prevent something like that.

Answer 1

It seems b is not an object, so I'd alert(b) before that line to see if it's been assigned a value at all.

Even if it has a value assigned, it may not be an object, so you might as well ask for typeof(b) == 'object'.

Answer 2

You are calling b.processId without making sure that b is an object.

Answer 3

Your variable b probably doesn’t exist. Try this:

var bPid = (typeof b != "undefined" && typeof b.processId == "number") ? b.processId : 0;

Answer 4

The safest (and the shortest) way to check if the b variable is 'truthy' (in Douglas Crockford's terms) would be

var bPid = (b && typeof (b.processId) == "number") ? b.processId : 0;

unless you explicitly want to compare it to null (in which case you should compare with === that doesn't do type coersion).

And to be 'truthy' a varible is anything except false, null, undefined, NaN, the number zero, or an empty string.