Home >Web Front-end >JS Tutorial >An article to talk about module path analysis in Node.js
This article will take you through the module path analysis in Node.js and introduce the Node module path analysis method. I hope it will be helpful to everyone!
Case
console.log(require.resolve(".")); // /Users/rainbow/Documents/前端/脚手架开发/rainbow-test/bin/index.js 输出bin/index.js的绝对路径 console.log(require.resolve.paths(".")); // [ '/Users/rainbow/Documents/前端/脚手架开发/rainbow-test/bin' ] 输出的文件可能在的路径的数组
console.log(require.resolve("yargs")); // /Users/rainbow/Documents/前端/脚手架开发/rainbow-test/node_modules/yargs/index.cjs console.log(require.resolve.paths("yargs")); /* [ '/Users/rainbow/Documents/前端/脚手架开发/rainbow-test/bin/node_modules', '/Users/rainbow/Documents/前端/脚手架开发/rainbow-test/node_modules', '/Users/rainbow/Documents/前端/脚手架开发/node_modules', '/Users/rainbow/Documents/前端/node_modules', '/Users/rainbow/Documents/node_modules', '/Users/rainbow/node_modules', '/Users/node_modules', '/node_modules', '/Users/rainbow/.node_modules', '/Users/rainbow/.node_libraries', '/usr/local/Cellar/node/14.3.0_1/lib/node' ] */
NodejsProject module path resolution is implemented through require.resolve.
method
The core process is:
method to generate possible paths for node_modules, if the incoming path is '/test/lerna/cli. js', add the path array of
node_moduels under each level path
,
Module._findPath The core process is:
cacheKey)
method, and combine
path and
request to form the file path basePath
exists, call
fs.realPahtSync to obtain the real path of the file
(key is cacheKey) (Module._pathCache is a map)
fs.realPahtSyncCore process:
require.resolve. paths is equivalent to
Module._resolveLookupPaths. This method obtains all possible paths of node_modules to form an array.
require.resolve.pathsThe implementation principle is:
(root path), return
directly ['/node_modules']
require('yargs')When
require method
method
Module.prototype.require = function(id) { //id = 'yargs' 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--; } };
// 参数 id = 'yargs' this={ paths: Module._nodeModulePaths(process.cwd()) }
Module._nodeModulePathsMethod
##
// 进入mac电脑所在的逻辑: // from => /Users/rainbow/Documents/前端/脚手架开发/lerna源码/lernas //'from' is the __dirname of the module. Module._nodeModulePaths = function(from) { from = path.resolve(from); // Return early not only to avoid unnecessary work, but to *avoid* returning // an array of two items for a root: [ '//node_modules', '/node_modules' ] if (from === '/') return ['/node_modules']; const paths = []; // 关键算法代码 for (let i = from.length - 1, p = 0, last = from.length; i >= 0; --i) { const code = from.charCodeAt(i); if (code === CHAR_FORWARD_SLASH) { 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; } } } // Append /node_modules to handle root paths. paths.push('/node_modules'); return paths; };Core algorithm analysis of for loop:
Module._loadMethod
The core implementation code is:
require.resolve
Project module path resolution is implemented through the require.resolve
method.
// node.js内置模块require的源代码 function resolve(request, options) { validateString(request, 'request'); return Module._resolveFilename(request, mod, false, options); //核心实现 } require.resolve = resolve; function paths(request) { validateString(request, 'request'); return Module._resolveLookupPaths(request, mod); //核心代码 } resolve.paths = paths;
Module._resolveFileNameCore process
Query the real path of the module through
Module._resolveFilename = function(request, parent, isMain, options) { if (NativeModule.canBeRequiredByUsers(request)) { //是否为内置模块 return request; } let paths; // 让paths和环境变量中的paths结合 paths = Module._resolveLookupPaths(request, parent); //核心代码 if (parent && parent.filename) { // 读取filename对应的package.json文件,看是否有exports字段,当前filename = false const filename = trySelf(parent.filename, request); if (filename) { //false const cacheKey = request + '\x00' + (paths.length === 1 ? paths[0] : paths.join('\x00')); Module._pathCache[cacheKey] = filename; return filename; } } //关键代码,找到本地执行文件 // Look up the filename first, since that's the cache key. const filename = Module._findPath(request, paths, isMain, false); if (filename) return filename; // ... };
Module._resolveLookupPahts
方法
require.resolve.paths("yargs")
核心实现方法生成
[ '/Users/rainbow/Documents/前端/脚手架开发/rainbow-test/bin/node_modules', '/Users/rainbow/Documents/前端/脚手架开发/rainbow-test/node_modules', '/Users/rainbow/Documents/前端/脚手架开发/node_modules', '/Users/rainbow/Documents/前端/node_modules', '/Users/rainbow/Documents/node_modules', '/Users/rainbow/node_modules', '/Users/node_modules', '/node_modules', '/Users/rainbow/.node_modules', '/Users/rainbow/.node_libraries', '/usr/local/Cellar/node/14.3.0_1/lib/node' ]
Module._resolveLookupPaths = function(request, parent) { if (NativeModule.canBeRequiredByUsers(request)) { debug('looking for %j in []', request); return null; } // Check for node modules paths. if (request.charAt(0) !== '.' || (request.length > 1 && request.charAt(1) !== '.' && request.charAt(1) !== '/' && (!isWindows || request.charAt(1) !== '\'))){ let paths = modulePaths; if (parent != null && parent.paths && parent.paths.length) { paths = parent.paths.concat(paths); } debug('looking for %j in %j', request, paths); return paths.length > 0 ? paths : null; } // In REPL, 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 in REPL there is no filename const mainPaths = ['.']; debug('looking for %j in %j', request, mainPaths); return mainPaths; } debug('RELATIVE: requested: %s from parent.id %s', request, parent.id); const parentDir = [path.dirname(parent.filename)]; debug('looking for %j', parentDir); return parentDir; };
Module._findPath
核心流程
\x00
合并生成cacheKey
)(\x00
是空格的16进制)Module._resolveLookupPahts
方法生成的paths
数组,将path
与request
组成文件路径basePath
fs.realPahtSync
获取文件的真实路径fs.realPahtSync
更多node相关知识,请访问:nodejs 教程!!
The above is the detailed content of An article to talk about module path analysis in Node.js. For more information, please follow other related articles on the PHP Chinese website!