TIL: Check for null or undefined in JS

While working on the metro codebase I found a curious convention enforced by their linter:

let foo = null;
let bar = undefined;
let baz = "";

foo == null; // => true
bar == null; // => true
baz == null; // => false

== null checks for nullor undefined which is incredibly common in JS. Notice it’s just two equal signs == which normally folks learn to avoid. I can’t believe I didn’t know this one.