import-local执行流程分析

import-local的作用

当全局node_modules和本地node_modules中，存在相同的库，则优先加载本地node_modules中的库

lerna入口文件：/cli.js

#!/usr/bin/env node

"use strict";

/* eslint-disable import/no-dynamic-require, global-require */
const importLocal = require("import-local");

if (importLocal(__filename)) {
  require("npmlog").info("cli", "using local version of lerna");
} else {
  require(".")(process.argv.slice(2));
}

import-local/index.js文件

'use strict';
const path = require('path');
const resolveCwd = require('resolve-cwd');
const pkgDir = require('pkg-dir');

module.exports = filename => {
    const globalDir = pkgDir.sync(path.dirname(filename));
    const relativePath = path.relative(globalDir, filename);
    const pkg = require(path.join(globalDir, 'package.json'));
    const localFile = resolveCwd.silent(path.join(pkg.name, relativePath));

    // Use `path.relative()` to detect local package installation,
    // because __filename's case is inconsistent on Windows
    // Can use `===` when targeting Node.js 8
    // See https://github.com/nodejs/node/issues/6624
    return localFile && path.relative(localFile, filename) !== '' ? require(localFile) : null;
};

执行lerna命令的流程

在本地lerna源文件目录lerna-main下执行* lerna ls*的流程分析

# 执行lerna 命令
> lerna ls
# 实际是通过which找到lerna的文件路径
> which lerna
/usr/local/bin/lerna # lerna软链接
> ll /usr/local/bin/lerna
# 软链接对应的真实地址 ：/usr/local/lib/node_modules/lerna/cli.js
lrwxr-xr-x  1 song  admin    32B 12 30 21:34 /usr/local/bin/lerna -> ../lib/node_modules/lerna/cli.js
# 所以执行 lerna ls 实际是执行下面的命令
> node /usr/local/lib/node_modules/lerna/cli.js ls

在lerna/cli.js 中最先执行import-lcoal

import-lcoal执行流程