Exploration into a batch() function for promises.

batch.js

var number = function (num) {
    return new Promise(function (resolve, reject) {
        if (typeof num !== 'number') {
            reject('invalid type');
        }
        setTimeout(function () { resolve(num); }, 2000);
    });
};

var batch = function () {
    var isError = false;
    var promises = [];

    Array.prototype.forEach.call(arguments, function (arg) {

        if (isError) {
                if (typeof arg !== 'function') {
                throw new Error('batch(Error, ...) function not found following Error keyword');
            }
            Promise.all(promises).catch(arg);
            promises = [];
            isError = false;
        }

        else if (arg === Error) {
            isError = true;
        }

        else if (typeof arg === 'function') {
            if (promises.length === 1 && promises[0] instanceof Promise) {
                promises = [
                    promises[0].then(
                        Function.prototype.call.bind(arg, null)
                    )
                ];
            }
            else {
                promises = [
                    Promise.all(promises).then(
                        Function.prototype.apply.bind(arg, null)
                    )
                ];
            }
        }

        else {
            promises.push(arg);
        }
    });
}

batch(
    // a batch accumulates promises until a handler function is provided
    number(5),
    
    // values don't have to be promises though
    7,
    function (x, y) { console.log('# adding ' + x + ' + ' + y + ' now'); return x + y; },
    
    // promises are implicitly chained
    function (x) { console.log('# result is ' + x); return x; },

    // a batch always accumulates including the last function return value
    number(9),
    function (v, w) { console.log(v * w, 'should be', 108); },
 
    // a batch is ready to handle any errors thrown along the way
    number ('A'),
    function (z) { console.log('I never make it to the screen, since A is not a number'); },

    // this is the syntax to handle errors
    Error, function (err) {
        console.warn('Oh no! I caught an error:', err);
    }
);

Thinking along the lines of this for angular etc:

batch(
    $http.get('/foo/bar'),
    $http.get('/bat/baz'),
    function (response1, response2) {
        $scope.value = [response1.data, response2.data];
        $scope.success = true;
    },
    Error, function (err) {
        $scope.success = false;
    }
);