Promise.serial() method

[rogierschouten]

Maybe add a library of these functions applicable to any ES6 promise, instead of putting them on Promise, but...

/**
 * Executes the callback for each value serially: the next callback starts once the previous has finished.
 * If any callback returns an error, the process is stopped and the error returned.
 */
export function tsSerial<T>(values: T[], callback: (value: T) => tsPromise.Promise<void>): tsPromise.Promise<void> {
    if (values.length === 0) {
        return tsPromise.Promise.resolve();
    }

    var i = 0;

    function doTail(): tsPromise.Promise<void> {
        var p = callback(values[i]);
        i++;
        if (i >= values.length) {
            return p;
        } else {
            return p.then((): tsPromise.Promise<void> => doTail());
        }
    }

    return doTail();
}