详解小程序循环require之坑

// a.jsconst B = require('./b.js');console.log('B in A', B);const A = {  name: 'A',  childName: B.name,};module.exports = A;

// b.jsconst C = require('./c.js');console.log('C in B', C);const B = {  name: 'B',  childName: C.name,}module.exports = B;

// c.jsconst A = require('./a.js');console.log('A in C', A);const C = {  name: 'C',  childName: A.name,};module.exports = C;

const fs = require('fs');const path = require('path');const fileCache = {};const requireLink = [];if (process.argv.length !== 3) { console.log(`please run as: node ${__filename.split(path.sep).pop()} file/to/track`); return;}const filePath = process.argv[2];const absFilePath = getFullFilePath(filePath);if (absFilePath) { resolveRequires(absFilePath, 0);} else { console.error('file not exist:', filePath);}/** * 递归函数，解析文件的依赖 * @param {String} file 引用文件的路径 * @param {Number} level 文件所在的引用层级 */function resolveRequires(file, level) { requireLink[level] = file; for (let i = 0; i < level; i ++) {  if (requireLink[i] === file) {   console.log('**** require circle detected ****');   console.log(requireLink.slice(0, level + 1));   console.log();   return;  } } const requireFiles = getRequireFiles(file); requireFiles.forEach(file => resolveRequires(file, level + 1));}/** * 获取文件依赖的文件 * @param {String} filePath 引用文件的路径 */function getRequireFiles(filePath) { if (!fileCache[filePath]) {  try {   const fileBuffer = fs.readFileSync(filePath);   fileCache[filePath] = fileBuffer.toString();  } catch(err) {   console.log('read file failed', filePath);   return [];  } } const fileContent = fileCache[filePath]; // 引入模块的几种形式 const requirePattern = /require/s*/(['"](.*?)['"]/)/g; const importPattern1 = /import/s+.*?/s+from/s+['"](.*?)['"]/g; const importPattern2 = /import/s+['"](.*?)['"]/g; const requireFilePaths = []; const baseDir = path.dirname(filePath); let match = null; while ((match = requirePattern.exec(fileContent)) !== null) {  requireFilePaths.push(match[1]); } while ((match = importPattern1.exec(fileContent)) !== null) {  requireFilePaths.push(match[1]); } while ((match = importPattern2.exec(fileContent)) !== null) {  requireFilePaths.push(match[1]); } return requireFilePaths.map(fp => getFullFilePath(fp, baseDir)).filter(fp => !!fp);}/** * 获取文件的完整绝对路径 * @param {String} filePath 文件路径 * @param {String} baseDir 文件路径的相对路径 */function getFullFilePath(filePath, baseDir) { if (baseDir) {  filePath = path.resolve(baseDir, filePath); } else {  filePath = path.resolve(filePath); } if (fs.existsSync(filePath)) {  const stat = fs.statSync(filePath);  if (stat.isDirectory() && fs.existsSync(path.join(filePath, 'index.js'))) {   return path.join(filePath, 'index.js');  } else if (stat.isFile()){   return filePath;  } } else if (fs.existsSync(filePath + '.js')) {  return filePath + '.js'; } return '';}