1.模块定义

(function () {    var modules = {};    // Stack of moduleIds currently being built.    var requireStack = [];    // Map of module ID -> index into requireStack of modules currently being built.    var inProgressModules = {};    var SEPARATOR = '.';    function build (module) {        var factory = module.factory;        var localRequire = function (id) {            var resultantId = id;            // Its a relative path, so lop off the last portion and add the id (minus "./")            if (id.charAt(0) === '.') {                resultantId = module.id.slice(0, module.id.lastIndexOf(SEPARATOR)) + SEPARATOR + id.slice(2);            }            return require(resultantId);        };        module.exports = {};        delete module.factory;        factory(localRequire, module.exports, module);        return module.exports;    }    require = function (id) {        if (!modules[id]) {            throw 'module ' + id + ' not found';        } else if (id in inProgressModules) {            var cycle = requireStack.slice(inProgressModules[id]).join('->') + '->' + id;            throw 'Cycle in require graph: ' + cycle;        }        if (modules[id].factory) {            try {                inProgressModules[id] = requireStack.length;                requireStack.push(id);                return build(modules[id]);            } finally {                delete inProgressModules[id];                requireStack.pop();            }        }        return modules[id].exports;    };    define = function (id, factory) {        if (modules[id]) {            throw 'module ' + id + ' already defined';        }        modules[id] = {            id: id,            factory: factory        };    };    define.remove = function (id) {        delete modules[id];    };    define.moduleMap = modules;})();