promise_test.js

class Checker {
    start() {
        if (this.checked) {
            this.stop();
        }
        this.checked = new Promise((resolve, reject) => {
            this.resolve = resolve;
            this.reject = reject;
        });
    }
    _clean() {
        this.checked = null;
        this.resolve = null;
        this.reject = null;
    }
    done() {
        if (this.resolve) {
            this.resolve();
            this._clean();
        }
    }
    stop() {
        if (this.reject) {
            this.reject();
            this._clean();
        }
    }
}

const checker = new Checker();
checker.start()
const checked = checker.checked
checked.then(() => {
    console.log('yatta!');
}).catch(() => {
    console.log('dameda!');
});

setTimeout(() => {
    let checked2 = checker.start();
    console.log(checked === checked2);
    checker.done();
    checker.stop();
}, 2000);
// というか、これは deferred https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Promise.jsm/Deferred