面试官：请实现一个通用函数把 callback 转成 promise

1. Node 加载采用什么模块
2. 获取 git 仓库所有 tags 的原理
3. 学会调试看源码
4. 学会面试高频考点 promisify 的原理和实现
5. 等等

循序渐进
借助调试
理清主线
查阅资料
总结记录

import remoteGitTags from 'remote-git-tags';

console.log(await remoteGitTags('https://github.com/lxchuan12/blog.git'));
//=> Map {'3.0.5' => '6020cc35c027e4300d70ef43a3873c8f15d1eeb2', …}

// package.json
{
  // 指定 Node 以什么模块加载，缺省时默认是 commonjs
 "type": "module",
 "exports": "./index.js",
  // 指定 nodejs 的版本
 "engines": {
  "node": "^12.20.0 || ^14.13.1 || >=16.0.0"
 },
 "scripts": {
  "test": "xo && ava"
 }
}

# 推荐克隆我的项目，保证与文章同步，同时测试文件齐全
git clone https://github.com/lxchuan12/remote-git-tags-analysis.git
# npm i -g yarn
cd remote-git-tags && yarn
# VSCode 直接打开当前项目
# code .

# 或者克隆官方项目
git clone https://github.com/sindresorhus/remote-git-tags.git
# npm i -g yarn
cd remote-git-tags && yarn
# VSCode 直接打开当前项目
# code .

// index.js
import {promisify} from 'node:util';
import childProcess from 'node:child_process';

const execFile = promisify(childProcess.execFile);

export default async function remoteGitTags(repoUrl) {
 const {stdout} = await execFile('git', ['ls-remote', '--tags', repoUrl]);
 const tags = new Map();

 for (const line of stdout.trim().split('\n')) {
  const [hash, tagReference] = line.split('\t');

  // Strip off the indicator of dereferenced tags so we can override the
  // previous entry which points at the tag hash and not the commit hash
  // `refs/tags/v9.6.0^{}` → `v9.6.0`
  const tagName = tagReference.replace(/^refs\/tags\//, '').replace(/\^{}$/, '');

  tags.set(tagName, hash);
 }

 return tags;
}

const execFile = promisify(childProcess.execFile);

examples
const imageSrc = 'https://www.themealdb.com/images/ingredients/Lime.png';

function loadImage(src, callback) {
    const image = document.createElement('img');
    image.src = src;
    image.alt = '公众号若川视野专用图？';
    image.style = 'width: 200px;height: 200px';
    image.onload = () => callback(null, image);
    image.onerror = () => callback(new Error('加载失败'));
    document.body.append(image);
}

loadImage(imageSrc, function(err, content){
  if(err){
    console.log(err);
    return;
  }
  console.log(content);
});

const loadImagePromise = function(src){
    return new Promise(function(resolve, reject){
        loadImage(src, function (err, image) {
            if(err){
                reject(err);
                return;
            }
            resolve(image);
        });
    });
};
loadImagePromise(imageSrc).then(res => {
    console.log(res);
})
.catch(err => {
    console.log(err);
});

function promisify(original){
    function fn(...args){
        return new Promise((resolve, reject) => {
            args.push((err, ...values) => {
                if(err){
                    return reject(err);
                }
                resolve(values);
            });
            // original.apply(this, args);
            Reflect.apply(original, this, args);
        });
    }
    return fn;
}

const loadImagePromise = promisify(loadImage);
async function load(){
    try{
        const res = await loadImagePromise(imageSrc);
        console.log(res);
    }
    catch(err){
        console.log(err);
    }
}
load();

const kCustomPromisifiedSymbol = SymbolFor('nodejs.util.promisify.custom');
const kCustomPromisifyArgsSymbol = Symbol('customPromisifyArgs');

let validateFunction;

function promisify(original) {
  // Lazy-load to avoid a circular dependency.
  if (validateFunction === undefined)
    ({ validateFunction } = require('internal/validators'));

  validateFunction(original, 'original');

  if (original[kCustomPromisifiedSymbol]) {
    const fn = original[kCustomPromisifiedSymbol];

    validateFunction(fn, 'util.promisify.custom');

    return ObjectDefineProperty(fn, kCustomPromisifiedSymbol, {
      value: fn, enumerable: false, writable: false, configurable: true
    });
  }

  // Names to create an object from in case the callback receives multiple
  // arguments, e.g. ['bytesRead', 'buffer'] for fs.read.
  const argumentNames = original[kCustomPromisifyArgsSymbol];

  function fn(...args) {
    return new Promise((resolve, reject) => {
      ArrayPrototypePush(args, (err, ...values) => {
        if (err) {
          return reject(err);
        }
        if (argumentNames !== undefined && values.length > 1) {
          const obj = {};
          for (let i = 0; i < argumentNames.length; i++)
            obj[argumentNames[i]] = values[i];
          resolve(obj);
        } else {
          resolve(values[0]);
        }
      });
      ReflectApply(original, this, args);
    });
  }

  ObjectSetPrototypeOf(fn, ObjectGetPrototypeOf(original));

  ObjectDefineProperty(fn, kCustomPromisifiedSymbol, {
    value: fn, enumerable: false, writable: false, configurable: true
  });
  return ObjectDefineProperties(
    fn,
    ObjectGetOwnPropertyDescriptors(original)
  );
}

promisify.custom = kCustomPromisifiedSymbol;