Module._resolveFilename 源码解析

Module._resolveFilename = function (request, parent, isMain, options) {
  if (
    StringPrototypeStartsWith(request, "node:") ||
    NativeModule.canBeRequiredByUsers(request)
  ) {
    return request;
  }

  let paths;

  if (typeof options === "object" && options !== null) {
    if (ArrayIsArray(options.paths)) {
      const isRelative =
        StringPrototypeStartsWith(request, "./") ||
        StringPrototypeStartsWith(request, "../") ||
        (isWindows && StringPrototypeStartsWith(request, ".\\")) ||
        StringPrototypeStartsWith(request, "..\\");

      if (isRelative) {
        paths = options.paths;
      } else {
        const fakeParent = new Module("", null);

        paths = [];

        for (let i = 0; i < options.paths.length; i++) {
          const path = options.paths[i];
          fakeParent.paths = Module._nodeModulePaths(path);
          const lookupPaths = Module._resolveLookupPaths(request, fakeParent);

          for (let j = 0; j < lookupPaths.length; j++) {
            if (!ArrayPrototypeIncludes(paths, lookupPaths[j]))
              ArrayPrototypePush(paths, lookupPaths[j]);
          }
        }
      }
    } else if (options.paths === undefined) {
      paths = Module._resolveLookupPaths(request, parent);
    } else {
      throw new ERR_INVALID_OPT_VALUE("options.paths", options.paths);
    }
  } else {
    paths = Module._resolveLookupPaths(request, parent);
  }

  if (parent && parent.filename) {
    if (request[0] === "#") {
      const pkg = readPackageScope(parent.filename) || {};
      if (
        pkg.data &&
        pkg.data.imports !== null &&
        pkg.data.imports !== undefined
      ) {
        try {
          return finalizeEsmResolution(
            packageImportsResolve(
              request,
              pathToFileURL(parent.filename),
              cjsConditions
            ),
            request,
            parent.filename,
            pkg.path
          );
        } catch (e) {
          if (e.code === "ERR_MODULE_NOT_FOUND")
            throw createEsmNotFoundErr(request);
          throw e;
        }
      }
    }
  }

  // Try module self resolution first
  const parentPath = trySelfParentPath(parent);
  const selfResolved = trySelf(parentPath, request);
  if (selfResolved) {
    const cacheKey =
      request +
      "\x00" +
      (paths.length === 1 ? paths[0] : ArrayPrototypeJoin(paths, "\x00"));
    Module._pathCache[cacheKey] = selfResolved;
    return selfResolved;
  }

  // Look up the filename first, since that's the cache key.
  const filename = Module._findPath(request, paths, isMain, false);
  if (filename) return filename;
  const requireStack = [];
  for (let cursor = parent; cursor; cursor = cursor.parent) {
    ArrayPrototypePush(requireStack, cursor.filename || cursor.id);
  }
  let message = `Cannot find module '${request}'`;
  if (requireStack.length > 0) {
    message =
      message +
      "\nRequire stack:\n- " +
      ArrayPrototypeJoin(requireStack, "\n- ");
  }
  // eslint-disable-next-line no-restricted-syntax
  const err = new Error(message);
  err.code = "MODULE_NOT_FOUND";
  err.requireStack = requireStack;
  throw err;
};

执行流程

1. 判断是否为内置模块 & 判断options

if (
    StringPrototypeStartsWith(request, "node:") ||
    NativeModule.canBeRequiredByUsers(request)
  ) {
    return request;
  }

if (typeof options === "object" && options !== null) {
    if (ArrayIsArray(options.paths)) {
      const isRelative =
        StringPrototypeStartsWith(request, "./") ||
        StringPrototypeStartsWith(request, "../") ||
        (isWindows && StringPrototypeStartsWith(request, ".\\")) ||
        StringPrototypeStartsWith(request, "..\\");

      if (isRelative) {
        paths = options.paths;
      } else {
        const fakeParent = new Module("", null);

        paths = [];

        for (let i = 0; i < options.paths.length; i++) {
          const path = options.paths[i];
          fakeParent.paths = Module._nodeModulePaths(path);
          const lookupPaths = Module._resolveLookupPaths(request, fakeParent);

          for (let j = 0; j < lookupPaths.length; j++) {
            if (!ArrayPrototypeIncludes(paths, lookupPaths[j]))
              ArrayPrototypePush(paths, lookupPaths[j]);
          }
        }
      }
    } else if (options.paths === undefined) {
      paths = Module._resolveLookupPaths(request, parent);
    } else {
      throw new ERR_INVALID_OPT_VALUE("options.paths", options.paths);
    }
  }

2. 查找更全的path

paths = Module._resolveLookupPaths(request, parent);

通过 Module._resolveLookupPaths 查找更全的路径

3. 解析真实路径

const filename = Module._findPath(request, paths, isMain, false);
if (filename) return filename;

如果解析到真实的路径返回路径