Minimal Events

evts.js

/**
 * Minimal Events
 * Copyright (c) 2013 marlun78
 * MIT License, https://gist.github.com/marlun78/bd0800cf5e8053ba9f83
 */

// TODO: Rework “once”
window.evts = (function () {
    
    'use strict';
    
    var MUST_BE_A_FUNCTION = 'The event handler must be a function',
        toString = {}.toString,
        map = {};

    function emit(type, data) {
        each(map[type], function (item, index, items) {
            item(data);
            if (item.__once__ === true) {
                delete item.__once__;
                remove(items, index);
            }
        });
    }

    function once(type, handler) {
        if (!isFunction(handler)) {
            throw new TypeError(MUST_BE_A_FUNCTION);
        }
        handler.__once__ = true; // Wont work if frozen...
        return on(type, handler);
    }

    function on(type, handler) {
        if (!isFunction(handler)) {
            throw new TypeError(MUST_BE_A_FUNCTION);
        }
        store(type, handler);
        return function () {
            off(type, handler);
        };
    }

    //Pass true as the second argument to remove all handlers of one type
    function off(type, handler) {
        if (handler === true) {
            map[type] = [];
            return;
        }
        each(map[type], function (item, index, items) {
            if (item === handler) {
                remove(items, index);
            }
        });
    }

    function store(type, handler) {
        if (!isArray(map[type])) {
            map[type] = [];
        }
        map[type].push(handler);
    }

    function remove(items, index) {
        items.splice(index, 1);
    }

    function each(items, iterator) {
        var index, count;
        for (index = 0, count = items.length; index < count; index++) {
            iterator(items[index], index, items);
        }
    }

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

    function isFunction(value) {
        return typeof value === 'function';
    }

    return {
        emit: emit,
        once: once,
        on: on,
        off: off
    };
}());