computedPrevious

computedPrevious is a helper function that returns a signal that emits the previous value of the passed signal. It’s useful when you want to keep track of the previous value of a signal. It will emit null as the previous value when the signal is first created.

import { computedPrevious } from 'ngxtension/computed-previous';

Usage

computedPrevious accepts a Signal and returns a Signal that emits the previous value of the passed Signal.

const a = signal(1);
const b = computedPrevious(a);

console.log(b()); // null

a.set(2);
console.log(b()); // 1

a.set(3);
console.log(b()); // 2

API

computedPrevious<T>(signal: Signal<T>): Signal<T | null>