aspect.js

/**
* Aspects for js (Function call interception)
* Released under the MIT License
* @copyright 2009 Vladimir Kolesnikov
* @author Vladimir Kolesnikov <voloko@gmail.com>
*/

var Aspect = new function() {

    this.add = function(obj, aspectName, aspect) {
        for (var selector in aspect) {
            if (!aspect.hasOwnProperty(selector)) continue;
            wrapMethod(obj, selector, aspect[selector])
        }
        obj.__aspects = obj.__aspects || {};
        obj.__aspects[aspectName] = aspect;
    },

    this.remove = function(obj, aspectName) {
        var aspect = obj.__aspects[aspectName],
        selector;
        for (selector in aspect) {
            if (!aspect.hasOwnProperty(selector)) continue;
            unwrapMethod(obj, selector, aspect[selector]);
        }
        delete obj.__aspects[aspectName];
    }

    function wrapMethod(obj, selector, wrapper) {
        var wrapperDescription = getWrapperDescription(selector),
        method, runBefore = false;

        method = obj[wrapperDescription.methodName];

        if (!method.__wrappers) {
            method = obj[wrapperDescription.methodName] = createInterceptor(method);
        };
        method.__wrappers[wrapperDescription.runBefore ? 'before' : 'after'].push(wrapper);
    }

    function unwrapMethod(obj, selector, wrapper) {
        var wrapperDescription = getWrapperDescription(selector),
        method = obj[wrapperDescription.methodName],
        wrappers = method.__wrappers;

        wrappers.before = without(wrappers.before, wrapper);
        wrappers.after  = without(wrappers.after, wrapper);
    }

    function getWrapperDescription(selector) {
        var match = selector.match(/^((after|before) )?(.*)$/);
        return {
            runBefore: !match || match[2] != "after",
            methodName: match ? match[3] : selector
        }
    }

    function without(array, item) {
        var result = [];
        for (var i=0, l = array.length; i < l; i++) {
            if (array[i] != item) result[result.length] = array[i];
        };
        return result;
    }

    function createInterceptor(method) {
        var interceptor = function() {
            for (var items = interceptor.__wrappers.before, l = items.length, i = 0; i < l; i++) {
                try{ 
                    items[i].apply(this, arguments); 
                } catch (e) { 
                    if (e instanceof AspectReturnException) return e.value;
                    throw e 
                }
            }
            var result = method.apply(this, arguments);

            for (items = interceptor.__wrappers.after, l = items.length, i = 0; i < l; i++) {
                try { 
                    items[i].apply(this, arguments); 
                } catch (e) { 
                    throw e;  
                }
            }
            return result;
        }
        interceptor.__wrappers = {
            before: [],
            after: []
        }
        return interceptor;
    }
};

var AspectReturnException = function(value) { this.value = value }