详解小程序循环require之坑

// a.js
const B = require('./b.js');

console.log('B in A', B);
const A = {
  name: 'A',
  childName: B.name,
};
module.exports = A;

// b.js
const C = require('./c.js');

console.log('C in B', C);
const B = {
  name: 'B',
  childName: C.name,
}
module.exports = B;

// c.js
const 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 '';
}