Problem with arrow function with Bangle.js

_ is just an identifier like a or A. There was - and still is the convention to name private things w/ a leading _ . _... means to leave it alone except you defined it in your scope.

I often use it var _=_||this; before a closures and as a space saver. The || is there to mess with the minifier in a good sense: if you use just var _ = this;, minifier tracks 'you' down and replaces the _ references in the code back to this, and - exactly - it is what you just tried to get away from...). Because Espruino interprets off the source, this as a source wastes 4 bytes... and if it shows often, it eats into the variables space.