Update var to let

[azimidev]

I thought it's a good idea to update var to let. I don't know if it's been done before in any PR and closed, but feel free to accept or reject. I'll try my best to make better PR every time. 🏆

[SanderMuller]

Why just use let and not use const where possible?

[azimidev]

@SanderMuller I was gonna use const I'm not sure if they like it.

some of those

var self = this;

are unnecessary if they use short arrow functions for instance.

[themsaid]

Hey, thanks for the PR but var is fine :)

[azimidev]

No worries mate.