判断某个文件名称(带后缀)数组中是否有一个文件是否在某个目录下，如果在，则返回这个文件名称(带后缀)，如果不在则返回 undefined

源码解析

"use strict";
const path = require("path");
const fs = require("fs");
const { promisify } = require("util");
const pLocate = require("p-locate");

const fsStat = promisify(fs.stat);
const fsLStat = promisify(fs.lstat);

const typeMappings = {
  directory: "isDirectory",
  file: "isFile",
};

function checkType({ type }) {
  if (type in typeMappings) {
    return;
  }

  throw new Error(`Invalid type specified: ${type}`);
}

const matchType = (type, stat) =>
  type === undefined || stat[typeMappings[type]]();

module.exports = async (paths, options) => {
  options = {
    cwd: process.cwd(),
    type: "file",
    allowSymlinks: true,
    ...options,
  };
  checkType(options);
  const statFn = options.allowSymlinks ? fsStat : fsLStat;

  return pLocate(
    paths,
    async (path_) => {
      try {
        const stat = await statFn(path.resolve(options.cwd, path_));
        return matchType(options.type, stat);
      } catch (_) {
        return false;
      }
    },
    options
  );
};

module.exports.sync = (paths, options) => {
  options = {
    cwd: process.cwd(),
    allowSymlinks: true,
    type: "file",
    ...options,
  };
  checkType(options);
  const statFn = options.allowSymlinks ? fs.statSync : fs.lstatSync;

  for (const path_ of paths) {
    try {
      const stat = statFn(path.resolve(options.cwd, path_));

      if (matchType(options.type, stat)) {
        return path_;
      }
    } catch (_) {}
  }
};

我们来分析一下同步 .sync 的源码部分

1. 定义并检查了 options 的 type

const typeMappings = {
	directory: 'isDirectory',
	file: 'isFile'
};

function checkType({type}) {
	if (type in typeMappings) {
		return;
	}

	throw new Error(`Invalid type specified: ${type}`);
}

...
options = {
  cwd: process.cwd(),
  allowSymlinks: true,
  type: 'file',
  ...options
};
checkType(options);

检查 type 是否在 typeMappings 中存在，否则爆出错误

2. 遍历查找目录中是否存在文件

const matchType = (type, stat) =>
  type === undefined || stat[typeMappings[type]]();
const statFn = options.allowSymlinks ? fs.statSync : fs.lstatSync;

for (const path_ of paths) {
  try {
    const stat = statFn(path.resolve(options.cwd, path_));

    if (matchType(options.type, stat)) {
      return path_;
    }
  } catch (_) {}
}

• 遍历传入的路径
• 解析传入的路径与当前遍历路径为绝对路径
• 通过fs.statSync 或者fs.lstatSync 方法获取文件信息状态
• 判断文件名称(带后缀)数组中是否有一个文件是否在某个目录下，如果在，则返回这个文件名称(带后缀)，如果不在则返回 undefined