Update tooltip.js

[tracker1]

Don't reference Tether via attachment to window, with the update one can import bootstrap providing the dependencies in webpack with:

new webpack.ProvidePlugin({
  $: 'jquery',
  jQuery: 'jquery',
  Tether: 'tether',
});

Then inside one's own bootstrap/globals, import 'bootstrap'; will simply work, and $/jQuery can be used from there.

I had wanted to do this, but also expose jQuery, Tether, etc when in development build in my code, but if I provide window.Tether, I can't then expose it to the outside...

[vsn4ik]

http://jsperf.com/is-undefined

[Johann-S]

Why not just : if (Tether === undefined) ?
Your JSPerf prove it's faster than using typeof

[tracker1]

@Johann-S That will throw an exception if Tether isn't defined...

if (someUndefinedValue === undefined) console.log('success')
// Uncaught ReferenceError someUndefinedValue is not defined

//this would work, but sloppier than the typeof
try {
  if (Tether){}
} catch(err) {
  throw new Error('Bootstrap tooltips require Tether (http://github.hubspot.com/tether/');
}

[tracker1]

@vsn4ik in your example undef is declared, its value is initially set to undefined so that the test passes... if you try to run a truly undefined/undeclared value (no var declaration)...

if (iHaveNotBeenReferencedOrDefinedAnywhere == undefined) console.log('you win');

You will see...

Uncaught ReferenceError iHaveNotBeenReferencedOrDefinedAnywhere is not defined

Since Tether is supposed to be declared in another library, and will be undeclared if it isn't included, then doing if (Tether === undefined) ... will throw an uncaught exception.

Not to mention that the test in this case is really contrived, as it is only run a single time when the file in question is loaded, not millions of iterations.

[mdo]

@bardiharborow @Johann-S Do we need this? I'm unclear if this helps us at all.

[bardiharborow]

I can't see any reason why we shouldn't merge this and close #20745. The issue here is that we want our code to work when Tether is loaded at both window.Tether (global, normal <script> inclusion) and Tether (local, webpack and various other bundlers). One of the many quirks with JavaScript is that member accesses (window.Tether) return undefined but local variable accesses throw an error. We can use typeof to work around that. I don't know why I didn't think of this as soon as I looked at #20745.