no-eq-null

value == null is true for null and also for undefined. If you meant only null, the check lets undefined through. If you meant both, the next reader can't tell that from the code.

Configure

Off by default. To turn it on:

[lint.rules]
"no-eq-null" = "error" # or "warn"

Examples

Reported:

if (user == null) {
  redirect("/login");
}

while (node != null) {
  node = node.next;
}

Not reported:

if (user === null) {
  redirect("/login");
}

if (session === null || session === undefined) {
  redirect("/login");
}

When not to use it

== null is a common shorthand for testing for null and undefined at once. If your code does that on purpose, leave this rule off. eqeqeq with the "smart" option allows == null and still reports value == other.