`Expecting a function in instanceof check, but got undefined` with .min file

[timothyallan]

I've just found that I get this only when I use gulp/browserify via npm in production mode. If I do a dev compile, it works fine!

Looks like it's failing on if(!(e instanceof t)) in the .min file, which is

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) in the regular one.

Any suggestions?

edit: It's not just the min file. I've taken the main JS now and am simply importing it. As soon as I add something as simple as this var myImpetus = new Impetus({ source: document.body, update: function(x, y) { // whatever you want to do with the values } });
everything breaks with Uncaught TypeError: Expecting a function in instanceof check, but got 1

I've got 40 other modules loading, and as soon as I remove Impetus, everything compiles!

[timothyallan]

Many hours later... It's uglify that's doing it, when set to mangle: { sort:true}
All the other options seem to work fine.

Only with Impetus though, which is bizarre.

[chrisbateman]

That's odd - I'll see if I can reproduce this and see what's going on...