As another borrowed convention, JS developers of yore (and likely some today still) used an _ prefix to denote “private” function/methods. Quotes as it’s just a convention - today JS supports # for actual private members in class syntax.
But doesn't it all trace back to C conventions anyways?
AS1 was plain ES3.
movieclip._x or movieclip._alpha (as in position and alpha blending) were accessed by properties with underscore to denote that you were using accessors (getters/setters).
Internally properties like Object.prototype.__proto__ had two underscores to denote they were private.
In AS2 you had:
class Foo extends Bar implements Xyz {
private foo
public function set x (value : Number) : void { ... }
public function get x () : Number { }
It's crazy to think it took us 10 years to reinvent the wheel with TypeScript.
AS3 was a complete rework, more akin to Java.
Programmers using underscore to denote identifiers for internal use was well-established and in use long before ActionScript even appeared. To claim that it's a "direct descendant" of ActionScript is arbitrary, anachronistic, and odd.
1. https://developers.google.com/apps-script/guides/html/commun...
So a variable that really ought to be named `class` you name `class_`.
A related conventional use of underscores in JS variable names is when "discarding" values in positional settings, like destructuring arrays.
E.g. `const [_, a, b] = triple`
In general, underscores in JS seem to be used to help call out what to ignore or what is less important.
But yeah for every other time most linters will accept _ as "ignore this".
Thanks for teaching me something today.