freduce/lib/index.js

The Zero-Dependency Left-To-Right Function Composer!

'use strict';

exports.__esModule = true;
var identity = function identity(x) {
    return x;
};
var always = function always(x) {
    return function () {
        return x;
    };
};

var isFunction = function isFunction(f) {
    return !!(f && f.constructor && f.call && f.apply);
};
var isReducible = function isReducible(a) {
    return !!(a && typeof a.reduce === 'function');
};
var isThenable = function isThenable(p) {
    return typeof p.then === 'function';
};

/**
 * freduce: Function Reducer
 * 
 * Composes from left-to-right, so d(c(b(a(x)))) is
 * equivalent to freduce(a,b,c,d)(x)
 *
 * @param {...Function} A list of functions
 * @returns {Function} A composite function
 */
var freduce = function freduce(first) {
    for (var _len = arguments.length, rest = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
        rest[_key - 1] = arguments[_key];
    }

    if (!first) return identity;
    if (isReducible(first)) first = freduce.apply(undefined, first);
    if (!isFunction(first)) return always(first);
    if (!rest) return first;
    return function () {
        return rest.reduce(reducer, first.apply(undefined, arguments));
    };
};

var reducer = exports.reducer = function reducer(previousResult, freddy) {
    var f = freduce(freddy);
    if (isThenable(previousResult)) return previousResult.then(f);

    return f(previousResult);
};

exports['default'] = freduce;