本文参加了由公众号@若川视野 发起的每周源码共读活动， 点击了解详情一起参与。

1.学习内容

参考文章：从 vue-cli 源码中，我发现27行读取 json 文件有趣的 npm 包
仓库地址 github.com/sindresorhu…

2.了解用法

官网举例其用法如下：

import {readPackage} from 'read-pkg';

console.log(await readPackage());
//=> {name: 'read-pkg', …}

console.log(await readPackage({cwd: 'some-other-directory'}));
//=> {name: 'unicorn', …}

API有：

readPackage(options?)
Returns a Promise<object> with the parsed JSON.

readPackageSync(options?)
Returns the parsed JSON.

3.猜测实现思路

使用node.js的fs模块读文件的内容；path模块解析路径

4.阅读源码

index.js:

import process from 'node:process';
import fs, {promises as fsPromises} from 'node:fs';
import path from 'node:path';
import {fileURLToPath} from 'node:url';
import parseJson from 'parse-json';
import normalizePackageData from 'normalize-package-data';

const toPath = urlOrPath => urlOrPath instanceof URL ? fileURLToPath(urlOrPath) : urlOrPath;

export async function readPackage({cwd, normalize = true} = {}) {
	cwd = toPath(cwd) || process.cwd();
	const filePath = path.resolve(cwd, 'package.json');
	const json = parseJson(await fsPromises.readFile(filePath, 'utf8'));

	if (normalize) {
		normalizePackageData(json);
	}

	return json;
}

export function readPackageSync({cwd, normalize = true} = {}) {
	cwd = toPath(cwd) || process.cwd();
	const filePath = path.resolve(cwd, 'package.json');
	const json = parseJson(fs.readFileSync(filePath, 'utf8'));

	if (normalize) {
		normalizePackageData(json);
	}

	return json;
}

异步方法使用了readFile，同步方法使用了readFileSync；都用到了parseJson解析；如果需要规范化则使用normalizePackageData。

流程图：

test.js:

import {fileURLToPath, pathToFileURL} from 'url';
import path from 'path';
import test from 'ava';
import {readPackage, readPackageSync} from '../index.js';

const dirname = path.dirname(fileURLToPath(import.meta.url));
process.chdir(dirname);
const rootCwd = path.join(dirname, '..');

test('async', async t => {
	const package_ = await readPackage();
	t.is(package_.name, 'unicorn');
	t.truthy(package_._id);
});

test('async - cwd option', async t => {
	const package_ = await readPackage({cwd: rootCwd});
	t.is(package_.name, 'read-pkg');
	t.deepEqual(
		await readPackage({cwd: pathToFileURL(rootCwd)}),
		package_,
	);
});

test('sync', t => {
	const package_ = readPackageSync();
	t.is(package_.name, 'unicorn');
	t.truthy(package_._id);
});

test('sync - cwd option', t => {
	const package_ = readPackageSync({cwd: rootCwd});
	t.is(package_.name, 'read-pkg');
	t.deepEqual(
		readPackageSync({cwd: pathToFileURL(rootCwd)}),
		package_,
	);
});