以前就觉得Nodejs的MooTools库很奇怪，因为用他的时候，不需要把require的返回值保存起来，今天实在憋不住，就研究了下，对NodeJs的require机制又有了几分深刻的理解。
MooTools库的“奇怪”用法：
require('mootools');
var QueryCommand = new Class({
initialize: function (product, week, action) {
this.product = product;
this.weeknum = week;
this.action = action;
},
toJsonString: function () {
return JSON.stringify(this);
}
});看到没，把require当作C++的include用了，之后的代码可以直接使用Class类型了。其实，MooTools的做法是把Class这个类型“附加”到了全局作用域。我觉得MooTools可能就是这么设计的，因为他是一个OO库嘛。
那么，MooTools是怎么把他自己附加到全局作用域的呢？其实很巧妙，是通过函数字面量做的：
(function(){
var Class = this.Class = new Type('Class', function(params){
if (instanceOf(params, Function)) params = {initialize: params};
var newClass = function(){
reset(this);
if (newClass.$prototyping) return this;
this.$caller = null;
var value = (this.initialize) ? this.initialize.apply(this, arguments) : this;
this.$caller = this.caller = null;
return value;
}.extend(this).implement(params);
newClass.$constructor = Class;
newClass.prototype.$constructor = newClass;
newClass.prototype.parent = parent;
return newClass;
});
......
})();
他通过函数字面量定义了一个匿名函数，然后立即执行之。这个是JS的惯用法。有一点要注意的是，在执行这个函数的时候，其实是没有this指针的！那么在函数内部使用this，访问的就是全局对象，就是那个始祖对象！
再看一个更加简单的例子：
app.js
require('./a.js')
console.log(a);a.js
a = 3; //输出3注意，上面不是var a=3;所以该语句实在全局作用域上附加了a这个属性（注意，也不是this！是始祖对象），然后呢，在app.js模块就能使用了。其实，在其他的模块也能访问了。
接下来说说，为什么会污染到全局作用域，nodejs不是用require来加载每个模块的嘛，模块应该互相独立的呀，其实nodeJs的模块加载顺序是这样的：
Module._load("xxx.js") --> var module = new Module(); --> module.load("xxx.js") --> module._compile() --> 最终调用的是被wrapper的模块代码，上面那个例子的话，最终执行的是：
(function (exports, require, module, __filename, __dirname) {
a = 3;
});看一下module.compile()的代码就清楚了：
// Returns exception if any
Module.prototype._compile = function(content, filename) {
var self = this;
// remove shebang
content = content.replace(/^\#\!.*/, '');
function require(path) {
return self.require(path);
}
require.resolve = function(request) {
return Module._resolveFilename(request, self);
};
Object.defineProperty(require, 'paths', { get: function() {
throw new Error('require.paths is removed. Use ' +
'node_modules folders, or the NODE_PATH ' +
'environment variable instead.');
}});
require.main = process.mainModule;
// Enable support to add extra extension types
require.extensions = Module._extensions;
require.registerExtension = function() {
throw new Error('require.registerExtension() removed. Use ' +
'require.extensions instead.');
};
require.cache = Module._cache;
var dirname = path.dirname(filename);
if (Module._contextLoad) {
if (self.id !== '.') {
debug('load submodule');
// not root module
var sandbox = {};
for (var k in global) {
sandbox[k] = global[k];
}
sandbox.require = require;
sandbox.exports = self.exports;
sandbox.__filename = filename;
sandbox.__dirname = dirname;
sandbox.module = self;
sandbox.global = sandbox;
sandbox.root = root;
return runInNewContext(content, sandbox, filename, true);
}
debug('load root module');
// root module
global.require = require;
global.exports = self.exports;
global.__filename = filename;
global.__dirname = dirname;
global.module = self;
return runInThisContext(content, filename, true);
}
// create wrapper function
var wrapper = Module.wrap(content);
var compiledWrapper = runInThisContext(wrapper, filename, true);
if (global.v8debug) {
if (!resolvedArgv) {
// we enter the repl if we're not given a filename argument.
if (process.argv[1]) {
resolvedArgv = Module._resolveFilename(process.argv[1], null);
} else {
resolvedArgv = 'repl';
}
}
// Set breakpoint on module start
if (filename === resolvedArgv) {
global.v8debug.Debug.setBreakPoint(compiledWrapper, 0, 0);
}
}
var args = [self.exports, require, self, filename, dirname];
return compiledWrapper.apply(self.exports, args);
};Module._contextLoad是false，所以有一些代码可以忽略掉，但里面有几个重点：
- 在函数入口处，定义了require函数，require函数还有一些静态的属性、成员函数。最终，require作为调用compiledWrapper.apply（）的一个实参。
- var wrapper其实是一个字符串类型的变量，值是 “(function (exports, require, module, __filename, __dirname) { ” + 你的模块代码 + "});"，就是上面我贴出来的那包装过的函数。最终，他通过调用runInThisContext()把字符串转成一个真正的函数。
- 最终通过调用被包装好的函数，执行你的模块代码。this指针指向的是self.exports，也就是module.exports，也就是exports。所以在你的模块内部：this === exports === module.exports。
- args是参数，再次重申：之所以你能在模块内部使用require（），是因为他是作为一个参数传入的。
exports其实是一个空的对象，所以exports的初值是空的，可以看这段代码：
function Module(id, parent) {
this.id = id;
this.exports = {};
this.parent = parent;
if (parent && parent.children) {
parent.children.push(this);
}
this.filename = null;
this.loaded = false;
this.children = [];
}最终是怎么把exports返回出来的呢，是在这个函数里面：
Module._load = function(request, parent, isMain) {
if (parent) {
debug('Module._load REQUEST ' + (request) + ' parent: ' + parent.id);
}
var filename = Module._resolveFilename(request, parent);
var cachedModule = Module._cache[filename];
if (cachedModule) {
return cachedModule.exports;
}
if (NativeModule.exists(filename)) {
// REPL is a special case, because it needs the real require.
if (filename == 'repl') {
var replModule = new Module('repl');
replModule._compile(NativeModule.getSource('repl'), 'repl.js');
NativeModule._cache.repl = replModule;
return replModule.exports;
}
debug('load native module ' + request);
return NativeModule.require(filename);
}
var module = new Module(filename, parent);
if (isMain) {
process.mainModule = module;
module.id = '.';
}
Module._cache[filename] = module;
var hadException = true;
try {
module.load(filename);
hadException = false;
} finally {
if (hadException) {
delete Module._cache[filename];
}
}
return module.exports;
};NodeJs调试一次不容易，把所有的代码，都贴上来（看看还蛮有收获的，有一个stripBOM工具函数，呵呵）：
(function (exports, require, module, __filename, __dirname) { // Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.
var NativeModule = require('native_module');
var Script = process.binding('evals').NodeScript;
var runInThisContext = Script.runInThisContext;
var runInNewContext = Script.runInNewContext;
var assert = require('assert').ok;
// If obj.hasOwnProperty has been overridden, then calling
// obj.hasOwnProperty(prop) will break.
// See: https://github.com/joyent/node/issues/1707
function hasOwnProperty(obj, prop) {
return Object.prototype.hasOwnProperty.call(obj, prop);
}
function Module(id, parent) {
this.id = id;
this.exports = {};
this.parent = parent;
if (parent && parent.children) {
parent.children.push(this);
}
this.filename = null;
this.loaded = false;
this.children = [];
}
module.exports = Module;
// Set the environ variable NODE_MODULE_CONTEXTS=1 to make node load all
// modules in thier own context.
Module._contextLoad = (+process.env['NODE_MODULE_CONTEXTS'] > 0);
Module._cache = {};
Module._pathCache = {};
Module._extensions = {};
var modulePaths = [];
Module.globalPaths = [];
Module.wrapper = NativeModule.wrapper;
Module.wrap = NativeModule.wrap;
var path = NativeModule.require('path');
Module._debug = function() {};
if (process.env.NODE_DEBUG && /module/.test(process.env.NODE_DEBUG)) {
Module._debug = function(x) {
console.error(x);
};
}
// We use this alias for the preprocessor that filters it out
var debug = Module._debug;
// given a module name, and a list of paths to test, returns the first
// matching file in the following precedence.
//
// require("a.")
// -> a.
//
// require("a")
// -> a
// -> a.
// -> a/index.
function statPath(path) {
var fs = NativeModule.require('fs');
try {
return fs.statSync(path);
} catch (ex) {}
return false;
}
// check if the directory is a package.json dir
var packageCache = {};
function readPackage(requestPath) {
if (hasOwnProperty(packageCache, requestPath)) {
return packageCache[requestPath];
}
var fs = NativeModule.require('fs');
try {
var jsonPath = path.resolve(requestPath, 'package.json');
var json = fs.readFileSync(jsonPath, 'utf8');
} catch (e) {
return false;
}
try {
var pkg = packageCache[requestPath] = JSON.parse(json);
} catch (e) {
e.path = jsonPath;
e.message = 'Error parsing ' + jsonPath + ': ' + e.message;
throw e;
}
return pkg;
}
function tryPackage(requestPath, exts) {
var pkg = readPackage(requestPath);
if (!pkg || !pkg.main) return false;
var filename = path.resolve(requestPath, pkg.main);
return tryFile(filename) || tryExtensions(filename, exts) ||
tryExtensions(path.resolve(filename, 'index'), exts);
}
// In order to minimize unnecessary lstat() calls,
// this cache is a list of known-real paths.
// Set to an empty object to reset.
Module._realpathCache = {};
// check if the file exists and is not a directory
function tryFile(requestPath) {
var fs = NativeModule.require('fs');
var stats = statPath(requestPath);
if (stats && !stats.isDirectory()) {
return fs.realpathSync(requestPath, Module._realpathCache);
}
return false;
}
// given a path check a the file exists with any of the set extensions
function tryExtensions(p, exts) {
for (var i = 0, EL = exts.length; i < EL; i++) {
var filename = tryFile(p + exts[i]);
if (filename) {
return filename;
}
}
return false;
}
Module._findPath = function(request, paths) {
var exts = Object.keys(Module._extensions);
if (request.charAt(0) === '/') {
paths = [''];
}
var trailingSlash = (request.slice(-1) === '/');
var cacheKey = JSON.stringify({request: request, paths: paths});
if (Module._pathCache[cacheKey]) {
return Module._pathCache[cacheKey];
}
// For each path
for (var i = 0, PL = paths.length; i < PL; i++) {
var basePath = path.resolve(paths[i], request);
var filename;
if (!trailingSlash) {
// try to join the request to the path
filename = tryFile(basePath);
if (!filename && !trailingSlash) {
// try it with each of the extensions
filename = tryExtensions(basePath, exts);
}
}
if (!filename) {
filename = tryPackage(basePath, exts);
}
if (!filename) {
// try it with each of the extensions at "index"
filename = tryExtensions(path.resolve(basePath, 'index'), exts);
}
if (filename) {
Module._pathCache[cacheKey] = filename;
return filename;
}
}
return false;
};
// 'from' is the __dirname of the module.
Module._nodeModulePaths = function(from) {
// guarantee that 'from' is absolute.
from = path.resolve(from);
// note: this approach *only* works when the path is guaranteed
// to be absolute. Doing a fully-edge-case-correct path.split
// that works on both Windows and Posix is non-trivial.
var splitRe = process.platform === 'win32' ? /[\/\\]/ : /\//;
// yes, '/' works on both, but let's be a little canonical.
var joiner = process.platform === 'win32' ? '\\' : '/';
var paths = [];
var parts = from.split(splitRe);
for (var tip = parts.length - 1; tip >= 0; tip--) {
// don't search in .../node_modules/node_modules
if (parts[tip] === 'node_modules') continue;
var dir = parts.slice(0, tip + 1).concat('node_modules').join(joiner);
paths.push(dir);
}
return paths;
};
Module._resolveLookupPaths = function(request, parent) {
if (NativeModule.exists(request)) {
return [request, []];
}
var start = request.substring(0, 2);
if (start !== './' && start !== '..') {
var paths = modulePaths;
if (parent) {
if (!parent.paths) parent.paths = [];
paths = parent.paths.concat(paths);
}
return [request, paths];
}
// with --eval, parent.id is not set and parent.filename is null
if (!parent || !parent.id || !parent.filename) {
// make require('./path/to/foo') work - normally the path is taken
// from realpath(__filename) but with eval there is no filename
var mainPaths = ['.'].concat(modulePaths);
mainPaths = Module._nodeModulePaths('.').concat(mainPaths);
return [request, mainPaths];
}
// Is the parent an index module?
// We can assume the parent has a valid extension,
// as it already has been accepted as a module.
var isIndex = /^index\.\w+?$/.test(path.basename(parent.filename));
var parentIdPath = isIndex ? parent.id : path.dirname(parent.id);
var id = path.resolve(parentIdPath, request);
// make sure require('./path') and require('path') get distinct ids, even
// when called from the toplevel js file
if (parentIdPath === '.' && id.indexOf('/') === -1) {
id = './' + id;
}
debug('RELATIVE: requested:' + request +
' set ID to: ' + id + ' from ' + parent.id);
return [id, [path.dirname(parent.filename)]];
};
Module._load = function(request, parent, isMain) {
if (parent) {
debug('Module._load REQUEST ' + (request) + ' parent: ' + parent.id);
}
var filename = Module._resolveFilename(request, parent);
var cachedModule = Module._cache[filename];
if (cachedModule) {
return cachedModule.exports;
}
if (NativeModule.exists(filename)) {
// REPL is a special case, because it needs the real require.
if (filename == 'repl') {
var replModule = new Module('repl');
replModule._compile(NativeModule.getSource('repl'), 'repl.js');
NativeModule._cache.repl = replModule;
return replModule.exports;
}
debug('load native module ' + request);
return NativeModule.require(filename);
}
var module = new Module(filename, parent);
if (isMain) {
process.mainModule = module;
module.id = '.';
}
Module._cache[filename] = module;
var hadException = true;
try {
module.load(filename);
hadException = false;
} finally {
if (hadException) {
delete Module._cache[filename];
}
}
return module.exports;
};
Module._resolveFilename = function(request, parent) {
if (NativeModule.exists(request)) {
return request;
}
var resolvedModule = Module._resolveLookupPaths(request, parent);
var id = resolvedModule[0];
var paths = resolvedModule[1];
// look up the filename first, since that's the cache key.
debug('looking for ' + JSON.stringify(id) +
' in ' + JSON.stringify(paths));
var filename = Module._findPath(request, paths);
if (!filename) {
var err = new Error("Cannot find module '" + request + "'");
err.code = 'MODULE_NOT_FOUND';
throw err;
}
return filename;
};
Module.prototype.load = function(filename) {
debug('load ' + JSON.stringify(filename) +
' for module ' + JSON.stringify(this.id));
assert(!this.loaded);
this.filename = filename;
this.paths = Module._nodeModulePaths(path.dirname(filename));
var extension = path.extname(filename) || '.js';
if (!Module._extensions[extension]) extension = '.js';
Module._extensions[extension](this, filename);
this.loaded = true;
};
Module.prototype.require = function(path) {
assert(typeof path === 'string', 'path must be a string');
assert(path, 'missing path');
return Module._load(path, this);
};
// Resolved path to process.argv[1] will be lazily placed here
// (needed for setting breakpoint when called with --debug-brk)
var resolvedArgv;
// Returns exception if any
Module.prototype._compile = function(content, filename) {
var self = this;
// remove shebang
content = content.replace(/^\#\!.*/, '');
function require(path) {
return self.require(path);
}
require.resolve = function(request) {
return Module._resolveFilename(request, self);
};
Object.defineProperty(require, 'paths', { get: function() {
throw new Error('require.paths is removed. Use ' +
'node_modules folders, or the NODE_PATH ' +
'environment variable instead.');
}});
require.main = process.mainModule;
// Enable support to add extra extension types
require.extensions = Module._extensions;
require.registerExtension = function() {
throw new Error('require.registerExtension() removed. Use ' +
'require.extensions instead.');
};
require.cache = Module._cache;
var dirname = path.dirname(filename);
if (Module._contextLoad) {
if (self.id !== '.') {
debug('load submodule');
// not root module
var sandbox = {};
for (var k in global) {
sandbox[k] = global[k];
}
sandbox.require = require;
sandbox.exports = self.exports;
sandbox.__filename = filename;
sandbox.__dirname = dirname;
sandbox.module = self;
sandbox.global = sandbox;
sandbox.root = root;
return runInNewContext(content, sandbox, filename, true);
}
debug('load root module');
// root module
global.require = require;
global.exports = self.exports;
global.__filename = filename;
global.__dirname = dirname;
global.module = self;
return runInThisContext(content, filename, true);
}
// create wrapper function
var wrapper = Module.wrap(content);
var compiledWrapper = runInThisContext(wrapper, filename, true);
if (global.v8debug) {
if (!resolvedArgv) {
// we enter the repl if we're not given a filename argument.
if (process.argv[1]) {
resolvedArgv = Module._resolveFilename(process.argv[1], null);
} else {
resolvedArgv = 'repl';
}
}
// Set breakpoint on module start
if (filename === resolvedArgv) {
global.v8debug.Debug.setBreakPoint(compiledWrapper, 0, 0);
}
}
var args = [self.exports, require, self, filename, dirname];
return compiledWrapper.apply(self.exports, args);
};
function stripBOM(content) {
// Remove byte order marker. This catches EF BB BF (the UTF-8 BOM)
// because the buffer-to-string conversion in `fs.readFileSync()`
// translates it to FEFF, the UTF-16 BOM.
if (content.charCodeAt(0) === 0xFEFF) {
content = content.slice(1);
}
return content;
}
// Native extension for .js
Module._extensions['.js'] = function(module, filename) {
var content = NativeModule.require('fs').readFileSync(filename, 'utf8');
module._compile(stripBOM(content), filename);
};
// Native extension for .json
Module._extensions['.json'] = function(module, filename) {
var content = NativeModule.require('fs').readFileSync(filename, 'utf8');
try {
module.exports = JSON.parse(stripBOM(content));
} catch (err) {
err.message = filename + ': ' + err.message;
throw err;
}
};
//Native extension for .node
Module._extensions['.node'] = process.dlopen;
// bootstrap main module.
Module.runMain = function() {
// Load the main module--the command line argument.
Module._load(process.argv[1], null, true);
// Handle any nextTicks added in the first tick of the program
process._tickCallback();
};
Module._initPaths = function() {
var isWindows = process.platform === 'win32';
if (isWindows) {
var homeDir = process.env.USERPROFILE;
} else {
var homeDir = process.env.HOME;
}
var paths = [path.resolve(process.execPath, '..', '..', 'lib', 'node')];
if (homeDir) {
paths.unshift(path.resolve(homeDir, '.node_libraries'));
paths.unshift(path.resolve(homeDir, '.node_modules'));
}
if (process.env['NODE_PATH']) {
var splitter = isWindows ? ';' : ':';
paths = process.env['NODE_PATH'].split(splitter).concat(paths);
}
modulePaths = paths;
// clone as a read-only copy, for introspection.
Module.globalPaths = modulePaths.slice(0);
};
// bootstrap repl
Module.requireRepl = function() {
return Module._load('repl', '.');
};
Module._initPaths();
// backwards compatibility
Module.Module = Module;
}); References:
- runInThisContext: http://www.cnblogs.com/rubylouvre/archive/2011/11/25/2262521.html
- Script.runInThisContext 以及nodejs的require: http://andy0807.iteye.com/blog/1446769
- 错误的或者过时的关于MooTools污染或防止污染全局作用域的文章，可以看出MooTools污染全局作用域可能是故意为之：http://davidwalsh.name/mootools-nodejs