WaitGroup.js

WaitGroup.js

class WaitGroup {

    constructor() {
        this.pending = 0;
        this.values = [];
        this.promise = Promise.resolve(this.values);
    }

    add(promise) {
        if (this.pending <= 0) {
            this.promise = new Promise((resolve, reject) => {
                this.resolve = resolve;
                this.reject = reject;
            });
        }

        var i = this.pending++;

        promise.then(
            (value) => {
                this.values[i] = value;
                if (--this.pending <= 0) {
                    this.resolve(this.values);
                }
            },
            (err) => {
                this.reject(err);
            }
        )
    }

    then(onFulfilled, onRejected) {
        return this.promise.then(onFulfilled, onRejected);
    }

    catch(onRejected) {
        return this.promise.catch(onRejected);
    }

}