WIP: Moving to arrow functions

[aviral243]

• Fixes Use arrow functions instead instead of normal ones #2198

• All functions that are called somewhere have been converted. However, functions used as a constructor e.g HelpWidget() should remain as it is because arrow functions cannot be used as constructors.

• I've also removed this binding wherever possible.

• Regarding testing: I've tried to test each file after conversion but try reporting any errors that might show up.

[fakela]

Good work `going on ... I will test the various files changed

[aviral243]

@fakela Thanks. That would be really helpful.

[aviral243]

Possible errors that might creep in include:

1. Lexical scoping of arrow functions i.e they are not hoisted so if any function is used before the declaration, an error would occur.

2. Use of arrow functions for an Object method.
   e.g.
   var obj = { x: 9, decrease: () => { this.x--; } }
   When calling obj.decrease, x will not decrease as this is not bound to anything.

3. Some functions have an argument passed named that, so care needs to taken not to replace them in haste.

4. Dynamic callbacks functions may also lead to some errors when using arrow functions, though I'm not very sure about it. I've used it in a couple of places till now and it seems to work fine.
   e.g.
   document.addEventListener("mousemove", (e) => { window.hasMouse = true; });

This can be used as a reference to track down possible errors, both by me and people reviewing.

[walterbender]

Maybe hold off working on js/blocks/* until #2196 lands. Otherwise, I imagine conflicts galore.

[aviral243]

Maybe hold off working on js/blocks/* until #2196 lands. Otherwise, I imagine conflicts galore.

I was thinking the same thing earlier today. Will hold it off.

[aviral243]

@walterbender Removed conflicts for now. ( Over 200 of them were present ). I think the work should be straightforward from here, touching only those files which keep getting merged as part of #2192

On that note, inside js/blocks/, since class components of different blocks need not be converted , the work is pretty minimal.

[aviral243]

I'm testing blocks mainly using the uber project used for testing Block API.

uber.zip

[walterbender]

Sorry about the conflicts. I accidentally merged something. Thanks for sorting it out.

[Ishakikani9117]

@walterbender Removed conflicts for now. ( Over 200 of them were present ). I think the work should be straightforward from here, touching only those files which keep getting merged as part of #2192

On that note, inside js/blocks/, since class components of different blocks need not be converted , the work is pretty minimal.

@aviral243 Please do the same thing for js/widgets and js/utils as you have done for blocks ,so none of us would have merge conflicts.

[aviral243]

Sorry about the conflicts. I accidentally merged something. Thanks for sorting it out.

@walterbender Not an issue there. They were mostly easy to resolve.

touching only those files which keep getting merged as part of #2192

Now following this strictly.