Y.Promise.each

promise-each.js

YUI.add('promise-each', function (Y) {

    function isArray(obj) {
        return Object.prototype.toString.call(obj) === '[object Array]';
    }

    function isFunction(obj) {
        return obj && (typeof obj === 'function');
    }

    Y.Promise.each = function (values, fn, context) {
        var Promise = this;
        // down the rabbit hole...
        return new Promise(function (resolve, reject) {
            if (!isArray(values)) {
                reject(new TypeError('Promise.each expects an array of values or promises'));
                return;
            }

            if (!isFunction(fn)) {
                reject(new TypeError('Promise.each expects an iterator function'));
                return;
            }

            var i = 0,
                length = values.length,
                remain = length,
                result = [],
                chains;

            function chain(index) {
                return Promise.resolve(values[index])
                    .then(function (value) {
                        // cache resolved value for final resolution
                        result[index] = value;

                        // call iterator without caching return values
                        fn.call(context, value, index, values);

                        if (--remain === 0) {
                            resolve(result);
                        }
                    }, reject)      // reject when promise rejects
                    .catch(reject); // reject when iterator throws
            }

            if (length < 1) {
                return resolve(result);
            }

            // start chain with first value
            chains = chain(i++);

            // chain the rest of the values
            for (; i < length; i++) {
                chains = chains.then(chain(i), reject);
            }
        });
    };

}, '', { requires: ['promise'] });

test-browser.js

YUI({
    modules: {
        'promise-each': {
            fullpath: './promise-each.js',
            requires: ['promise']
        }
    }
}).use('promise-each', function (Y) {
    Y.Promise.each(['foo', 'bar', Y.when('teapot'), 'baz'], function (val, idx) {
        if (idx === 1) {
            throw new Error('threw at index 1');
        }
        Y.log('"' + val + '" at index %d' + idx);
    })
        .then(function (result) {
            Y.log(result);
        })
        .catch(function (ex) {
            Y.error(ex);
        });
});

test-node.js

#!/usr/bin/env node

var path = require('path');
var YUI = require('yui').YUI;

var Y = YUI({
    useSync: true,
    modules: {
        'promise-each': {
            fullpath: path.join(__dirname, 'promise-each.js'),
            requires: ['promise']
        }
    }
}).use('promise-each');

Y.Promise.each(['foo', 'bar', Y.when('teapot'), 'baz'], function (val, idx) {
    if (idx === 1) {
        throw new Error('BOOM at index 1');
    }
    console.log('"%s" at index %d', val, idx);
})
    .then(function (result) {
        console.log('result', result);
    })
    .catch(function (ex) {
        console.error(ex);
    });