@dualjack/svelte-tools/dist/tools/watch/watch.svelte.js

### Why? Because runes are not safe to toss around by design.

export default function watch(src, cb, options) {
    let isPaused = $state(false);
    let oldValue;
    let isLazyPass = false;
    function run(newValue) {
        if (isPaused)
            return;
        //  Run once and change the flag.
        if (options?.lazy && !isLazyPass) {
            isLazyPass = true;
            return;
        }
        cb(newValue, oldValue);
        oldValue = newValue;
    }
    $effect.root(() => {
        if (options?.pre) {
            //  Pre - before DOM modifications.
            $effect.pre(() => {
                run(src());
            });
        }
        else {
            //  After DOM modifications.
            $effect(() => {
                run(src());
            });
        }
    });
    return {
        pause: () => isPaused = true,
        resume: () => isPaused = false,
        isPaused: {
            get current() { return isPaused; },
            set current(v) { isPaused = v; },
        },
    };
}