Tip sharing: Elegantly obtain the package.json file

In daily development, we all know that package.json is a description of a project or module package, which contains a lot of meta-information. So how should we read package.json to obtain the information inside? What comes into play is our protagonist today - read-pkg. The key source code is only about 30 lines. Next, let’s take a closer look at the implementation, which can be regarded as laying the foundation for the subsequent development of our own toolkit! [Related tutorial recommendations: nodejs video tutorial]

Harvest list

• Debugging source code
• Elegantly obtain package.json
• Standardize package metadata
• Application of import.meta.url

Preschool Prepare

Download the source code

git clone https://github.com/sindresorhus/read-pkg.git
cd read-pkg&&yarn

General source code learning first looks at README.md and package.json, The readme teaches usage, and package.json will indicate the command. Generally, we start debugging from the script of package.json. Here is a screenshot:

This is the first time I have seen this command. Maybe you don’t know what it wants to express. If you look down at devDependencies, you can see that the three commands correspond to three packages. Don’t know what the packages are for? Go to Baidu by yourself, general package usage can be found on npm

• ava
  

node.js test package

• ##tsd
  

Detect ts type

##xo
• 
  

(ESLint wrapper), with good defaults

Source code debugging analysis

Set a breakpoint in the entry file in advance, and then click the

Debug Script

button in the script of package.json to enable debugging. If there is no such button, you may need to update vscode.

Source code structure analysis

Introduction of dependencies

• // node进程
  import process from 'node:process';
  // fs文件模块
  import fs, {promises as fsPromises} from 'node:fs';
  // path 路径模块
  import path from 'node:path';
  // url模块
  import {fileURLToPath} from 'node:url';
  // 解析json，并且会伴随有用的报错，https://github.com/sindresorhus/parse-json#readme
  import parseJson from 'parse-json';
  // 规范化包元数据 https://github.com/npm/normalize-package-data#readme
  import normalizePackageData from 'normalize-package-data';

Convert url to file path

• // fileURLToPath将url转化为文件路径
  const toPath = urlOrPath => urlOrPath instanceof URL ? fileURLToPath(urlOrPath) : urlOrPath;

As debugging comes to the test file, there are several concepts that can be seen in many source codes, so they are worthy of our attention. They are analyzed below:

import.meta.url

Mainly applied to __filename and __dirname which are not available in ES module

path.dirname

Used to obtain the directory name of the specified path

fileURLToPath(import.meta.url )

Extraction path

process.chdir

    更改Node.js进程的当前工作目录，或者在执行失败时抛出异常(例如，如果指定的目录不存在)。

• readPackage方法(异步读取)

export async function readPackage({cwd, normalize = true} = {}) {
// 默认用process.cwd获取当前工作目录，获取工作目录
    cwd = toPath(cwd) || process.cwd();
// 获取package.json相对当前工作目录的绝对路径
    const filePath = path.resolve(cwd, 'package.json');
// 异步读取package.json并解析，fsPromises异步文件模块
    const json = parseJson(await fsPromises.readFile(filePath, 'utf8'));
   // 规范化包元数据
    if (normalize) {
        normalizePackageData(json);
    }


    return json;

}

• readPackageSync方法（同步读取）

export function readPackageSync({cwd, normalize = true} = {}) {
   // 默认用process.cwd获取当前工作目录，获取工作目录
    cwd = toPath(cwd) || process.cwd();
   // 获取package.json相对当前工作目录的绝对路径
    const filePath = path.resolve(cwd, 'package.json');
   // 读取package.json并解析
    const json = parseJson(fs.readFileSync(filePath, 'utf8'));

    // 序列化元数据
    if (normalize) {

        normalizePackageData(json);

    }


    return json;

}

• normalizePackageData作用

序列化前

序列化后

    调试后发现序列化后会生成_id,对应测试用例中的t.truthy(package_._id)

总结

    今天下载并调试了read-pkg的源码，进一步了解了nodejs的path、url、process模块对于读取文件的应用，read-pkg麻雀虽小五脏俱全，完整的测试用例也是我们可以在自己的工具包中借鉴使用的！今天刚好是国庆，追梦人们国庆快乐哇~

更多node相关知识，请访问：nodejs 教程！

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