Patches Meteor.subscribe and Tracker.autorun to stop when a Svelte component is destroyed. Also supports await block for subscriptions.

svelte-hooks.js

import { current_component } from 'svelte/internal';

_autorun = Tracker.autorun;
Tracker.autorun = function autorun() {
    const computation = _autorun.apply(this, arguments);
    if (current_component) {
        current_component.$$.on_destroy.push(computation.stop.bind(computation));
    }
    return computation;
};

_subscribe = Meteor.subscribe;
Meteor.subscribe = function subscribe(name) {
    const params = Array.from(arguments);
    let callbacks = Object.create(null);
    if (params.length > 1) {
        // Preserve existing callbacks.
        // Last arg may be specified as a function, or as an object
        const last = params[params.length - 1];
        if (typeof last === 'function') {
            callbacks.onReady = params.pop();
        } else if (last && [last.onReady, last.onError, last.onStop].some(f => typeof f === "function")) {
            callbacks = params.pop();
        }
    }
    params.push(callbacks);

    let subscription;

    // Collect callbacks to call when subscription is ready or has errored.
    let readyCallbacks = [];
    let errorCallbacks = [];
    if (callbacks.onReady) {
        readyCallbacks.push(callbacks.onReady);
    }
    if (callbacks.onError) {
        errorCallbacks.push(callbacks.onError);
    }
    callbacks.onReady = () => {
        readyCallbacks.forEach(fn => fn(subscription));
        readyCallbacks.length = 0;
    };
    callbacks.onError = (err) => {
        errorCallbacks.forEach(fn => fn(err));
        errorCallbacks.length = 0;
    };

    subscription = _subscribe.apply(this, params);
    if (current_component) {
        current_component.$$.on_destroy.push(subscription.stop.bind(subscription));
    }
    subscription.then = (fn, err) => {
        readyCallbacks.push(fn);
        err && errorCallbacks.push(err);
    };
    return subscription;
};