Nodejs模块化实现示例深入探究

const fs = require('fs')

// add.js
exports.add = function(a, b) {
return a + b
}

const { add } = require('./add.js')
add(1, 2) // print 3

// Loads a module at the given file path. Returns that module's
// `exports` property.
Module.prototype.require = function(id) {
validateString(id, 'id');
if (id === '') {
throw new ERR_INVALID_ARG_VALUE('id', id,
'must be a non-empty string');
}
requireDepth++;
try {
return Module._load(id, this, /* isMain */ false);
} finally {
requireDepth--;
}
};

Module._cache = Object.create(null);
// 这里先定义了一个缓存的对象
// ... ...
// Check the cache for the requested file.
// 1. If a module already exists in the cache: return its exports object.
// 2. If the module is native: call
//    `NativeModule.prototype.compileForPublicLoader()` and return the exports.
// 3. Otherwise, create a new module for the file and save it to the cache.
//    Then have it load  the file contents before returning its exports
//    object.
Module._load = function(request, parent, isMain) {
let relResolveCacheIdentifier;
if (parent) {
debug('Module._load REQUEST %s parent: %s', request, parent.id);
// Fast path for (lazy loaded) modules in the same directory. The indirect
// caching is required to allow cache invalidation without changing the old
// cache key names.
relResolveCacheIdentifier = `${parent.path}\x00${request}`;
const filename = relativeResolveCache[relResolveCacheIdentifier];
if (filename !== undefined) {
const cachedModule = Module._cache[filename];
if (cachedModule !== undefined) {
updateChildren(parent, cachedModule, true);
return cachedModule.exports;
}
delete relativeResolveCache[relResolveCacheIdentifier];
}
}
const filename = Module._resolveFilename(request, parent, isMain);
const cachedModule = Module._cache[filename];
if (cachedModule !== undefined) {
updateChildren(parent, cachedModule, true);
return cachedModule.exports;
}
const mod = loadNativeModule(filename, request, experimentalModules);
if (mod && mod.canBeRequiredByUsers) return mod.exports;
// Don't call updateChildren(), Module constructor already does.
const module = new Module(filename, parent);
if (isMain) {
process.mainModule = module;
module.id = '.';
}
Module._cache[filename] = module;
if (parent !== undefined) {
relativeResolveCache[relResolveCacheIdentifier] = filename;
}
let threw = true;
try {
module.load(filename);
threw = false;
} finally {
if (threw) {
delete Module._cache[filename];
if (parent !== undefined) {
delete relativeResolveCache[relResolveCacheIdentifier];
}
}
}
return module.exports;
};

console.log(module.paths)

node module_path.js

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.
// return root node_modules when path is 'D:\\'.
// path.resolve will make sure from.length >=3 in Windows.
if (from.charCodeAt(from.length - 1) === CHAR_BACKWARD_SLASH &&
from.charCodeAt(from.length - 2) === CHAR_COLON)
return [from + 'node_modules'];
const paths = [];
var p = 0;
var last = from.length;
for (var i = from.length - 1; i >= 0; --i) {
const code = from.charCodeAt(i);
// The path segment separator check ('\' and '/') was used to get
// node_modules path for every path segment.
// Use colon as an extra condition since we can get node_modules
// path for drive root like 'C:\node_modules' and don't need to
// parse drive name.
if (code === CHAR_BACKWARD_SLASH ||
code === CHAR_FORWARD_SLASH ||
code === CHAR_COLON) {
if (p !== nmLen)
paths.push(from.slice(0, last) + '\\node_modules');
last = i;
p = 0;
} else if (p !== -1) {
if (nmChars[p] === code) {
++p;
} else {
p = -1;
}
}
}
return paths;
};

// require('./internal/constants.js')
require('./internal/constants')

if (!filename) {
// Try it with each of the extensions
if (exts === undefined)
exts = Object.keys(Module._extensions);
filename = tryExtensions(basePath, exts, isMain);
}

// Given a path, check if the file exists with any of the set extensions
function tryExtensions(p, exts, isMain) {
for (var i = 0; i < exts.length; i++) {
const filename = tryFile(p + exts[i], isMain);
if (filename) {
return filename;
}
}
return false;
}

function tryFile(requestPath, isMain) {
const rc = stat(requestPath);
if (preserveSymlinks && !isMain) {
return rc === 0 && path.resolve(requestPath);
}
return rc === 0 && toRealPath(requestPath);
}
// Check if the file exists and is not a directory
// if using --preserve-symlinks and isMain is false,
// keep symlinks intact, otherwise resolve to the
// absolute realpath.
function tryFile(requestPath, isMain) {
const rc = stat(requestPath);
if (preserveSymlinks && !isMain) {
return rc === 0 && path.resolve(requestPath);
}
return rc === 0 && toRealPath(requestPath);
}
// 这个函数在其他地方还有用到，比较重要
function toRealPath(requestPath) {
return fs.realpathSync(requestPath, {
[internalFS.realpathCacheKey]: realpathCache
});
}

function Module(id = '', parent) {
this.id = id;
this.path = path.dirname(id);
this.exports = {};
this.parent = parent;
updateChildren(parent, this, false);
this.filename = null;
this.loaded = false;
this.children = [];
}

// Enable support to add extra extension types.require.extensions = Module._extensions;

console.log(require.extensions)
// { '.js': [Function], '.json': [Function], '.node': [Function] }

const fs = require('fs')
// 注册解析方法到 require.extensions 对象
require.extensions['.csv'] = function(module, filename) {
// module 是当前模块的 Module 实例，filename 是当前文件模块的路径
const content = fs.readFileSync(filename, 'utf8'),
lines = content.split(/\r\n/)
const res = lines.map(line => line.split(','))
// 注意导出是通过给 module.exports 赋值，而不是用 return
module.exports = res
}
/*
*    demo.csv 的内容为：
*    1,2,3
*    2,3,4
*    5,6,7
*/
const arr = require('./demo.csv')
console.log(arr)
// output
// [ [ '1', '2', '3' ], [ '2', '3', '4' ], [ '5', '6', '7' ] ]

exports.add = (a, b) => a + b

(function(exports, require, module, __filename, __dirname) {
exports.add = (a, b) => a + b
})

function changeRef(obj) {
obj = 12
}
const ref = {}
changeRef(ref)
console.log(ref) // {}

// Native extension for .js
Module._extensions['.js'] = function(module, filename) {
const content = fs.readFileSync(filename, 'utf8');
module._compile(content, filename);
};

// Run the file contents in the correct scope or sandbox. Expose
// the correct helper variables (require, module, exports) to
// the file.
// Returns exception, if any.Module.prototype._compile = function(content, filename) {
let moduleURL;
let redirects;
if (manifest) {
moduleURL = pathToFileURL(filename);
redirects = manifest.getRedirects(moduleURL);
manifest.assertIntegrity(moduleURL, content);
}
const compiledWrapper = wrapSafe(filename, content);
var inspectorWrapper = null;
if (getOptionValue('--inspect-brk') && process._eval == null) {
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, false);
} else {
resolvedArgv = 'repl';
}
}
// Set breakpoint on module start
if (!hasPausedEntry && filename === resolvedArgv) {
hasPausedEntry = true;
inspectorWrapper = internalBinding('inspector').callAndPauseOnStart;
}
}
const dirname = path.dirname(filename);
const require = makeRequireFunction(this, redirects);
var result;
const exports = this.exports;
const thisValue = exports;
const module = this;
if (requireDepth === 0) statCache = new Map();
if (inspectorWrapper) {
result = inspectorWrapper(compiledWrapper, thisValue, exports,
require, module, filename, dirname);
} else {
result = compiledWrapper.call(thisValue, exports, require, module,
filename, dirname);
}
if (requireDepth === 0) statCache = null;
return result;
};

const compiledWrapper = wrapSafe(filename, content);

function wrapSafe(filename, content) {
if (patched) {
const wrapper = Module.wrap(content);
return vm.runInThisContext(wrapper, {
filename,
lineOffset: 0,
displayErrors: true,
importModuleDynamically: experimentalModules ? async (specifier) => {
const loader = await asyncESM.loaderPromise;
return loader.import(specifier, normalizeReferrerURL(filename));
} : undefined,
});
}
const compiled = compileFunction(
content,
filename,
0,
0,
undefined,
false,
undefined,
[],
[
'exports',
'require',
'module',
'__filename',
'__dirname',
]
);
if (experimentalModules) {
const { callbackMap } = internalBinding('module_wrap');
callbackMap.set(compiled.cacheKey, {
importModuleDynamically: async (specifier) => {
const loader = await asyncESM.loaderPromise;
return loader.import(specifier, normalizeReferrerURL(filename));
}
});
}
return compiled.function;
}
// Module.wrap
// eslint-disable-next-line func-style
let wrap = function(script) {
return Module.wrapper[0] + script + Module.wrapper[1];
};
const wrapper = [
'(function (exports, require, module, __filename, __dirname) { ',
'\n});'
];
Object.defineProperty(Module, 'wrap', {
get() {
return wrap;
},
set(value) {
patched = true;
wrap = value;
}
});