Question

Why does the following line sometimes yield the message “undefined is not a function” in the chrome dev console:

(callbackOrUndefined || function() {})();

The idea is to execute callback if it is truthy, i.e. a function, otherwise execute the empty function.

I had to replace it with :

if (callbackOrUndefined !== undefined) callbackOrUndefined();

Edit: I guess I wasn’t clear enough. It sometimes seem to evaluate the block to undefined(); and I don’t understand how and why.

Answer 1

That’s because callbackOrUndefined has a falsy value and then the null function is selected, and when called, it returns undefined.

Notice that you may get undefined even if callbackOrUndefined doesn’t return a defined value…