UNINITIALIZED

See source code

A special symbol used to indicate that a computed signal has not been initialized yet. This is passed as the previousValue parameter to a computed signal function on its first run.

UNINITIALIZED: unique symbol;

Example

const count = atom("count", 0);
const double = computed("double", (prevValue) => {
  if (isUninitialized(prevValue)) {
    console.log("First computation!");
  }
  return count.get() * 2;
});

RESET_VALUE

WithDiff