jslib/lib/function.js

'use strict';

const toArray = require('./array').toArray;

const argsToArray = fn => {
    // must not be a fat arrow since it breaks the arguments
    return function () {
        return fn(toArray(arguments));
    };
};

const curry = fn => {
    return function curried () {
        const that = this,
            args = Array.prototype.slice.call(arguments);

        if (args.length < fn.length) {
            return curried.bind.apply(curried, [that].concat(args));
        } else {
            return fn.apply(that, args);
        }
    };
};

const combine = argsToArray(fns => fns.reverse().reduce((fnc, fn) => val => fnc(fn(val))));

// cannot use fat arrow function since we don't get the arguments, then
const promisify = (fn, context = null) => function () {
    // copy passed arguments to a new array
    const args = toArray(arguments);

    return new Promise((resolve, reject) => {
        // add a callback to the arguments, which resolves the promise with the result
        args.push((err, data) => {
            if (err) {
                reject(err);
            } else {
                resolve(data);
            }
        });

        // call the original function with our callback flavoured arguments
        fn.apply(context, args);
    });
};

/**
 returns a function which executes promises one after another
 @param promiseGenerators an array of functions which return a promise
 @return function which executes the promises
 */
const enqueue = (promiseGenerators) => {
    return promiseGenerators.reduce((f, promiseGenerator) => {
        return () => {
            return f().then(promiseGenerator);
        };
    });
};

/**
 Returns a function which executes promises one after another. The resulting function
 returns a promise, which gets filled with an array of the results of the single promises.
 @param promiseGenerators an array of functions which return a promise
 @return function which executes the promises
 */
const enqueueWithResults = (function () {
    const fnQueue = (results, promiseGenerators) => promiseGenerators.reduce((f, promiseGenerator) => {
        return () => {
            return f().then(result => {
                results.push(result);
                return promiseGenerator();
            });
        };
    });

    return function (promiseGenerators) {
        return () => {
            const results = [];
            return fnQueue(results, promiseGenerators)().then(result => {
                results.push(result);
                return results;
            });
        };
    };
}());

module.exports = {
    argsToArray,
    combine,
    curry,
    promisify,
    enqueue,
    enqueueWithResults
};