函数checkThatNpmCanReadCwd
函数名的含义:检查 Npm 是否可以读取 Cwd
首先看下源码
const spawn = require('cross-spawn');
// See https://github.com/facebook/create-react-app/pull/3355
function checkThatNpmCanReadCwd() {
const cwd = process.cwd();
let childOutput = null;
try {
// Note: intentionally using spawn over exec since
// the problem doesn't reproduce otherwise.
// `npm config list` is the only reliable way I could find
// to reproduce the wrong path. Just printing process.cwd()
// in a Node process was not enough.
childOutput = spawn.sync('npm', ['config', 'list']).output.join('');
} catch (err) {
// Something went wrong spawning node.
// Not great, but it means we can't do this check.
// We might fail later on, but let's continue.
return true;
}
if (typeof childOutput !== 'string') {
return true;
}
const lines = childOutput.split('\n');
// `npm config list` output includes the following line:
// "; cwd = C:\path\to\current\dir" (unquoted)
// I couldn't find an easier way to get it.
const prefix = '; cwd = ';
const line = lines.find(line => line.startsWith(prefix));
if (typeof line !== 'string') {
// Fail gracefully. They could remove it.
return true;
}
const npmCWD = line.substring(prefix.length);
if (npmCWD === cwd) {
return true;
}
console.error(
chalk.red(
`Could not start an npm process in the right directory.\n\n` +
`The current directory is: ${chalk.bold(cwd)}\n` +
`However, a newly started npm process runs in: ${chalk.bold(
npmCWD
)}\n\n` +
`This is probably caused by a misconfigured system terminal shell.`
)
);
if (process.platform === 'win32') {
console.error(
chalk.red(`On Windows, this can usually be fixed by running:\n\n`) +
` ${chalk.cyan(
'reg'
)} delete "HKCU\\Software\\Microsoft\\Command Processor" /v AutoRun /f\n` +
` ${chalk.cyan(
'reg'
)} delete "HKLM\\Software\\Microsoft\\Command Processor" /v AutoRun /f\n\n` +
chalk.red(`Try to run the above two lines in the terminal.\n`) +
chalk.red(
`To learn more about this problem, read: https://blogs.msdn.microsoft.com/oldnewthing/20071121-00/?p=24433/`
)
);
}
return false;
}
函数内核心代码含义解读
childOutput = spawn.sync('npm', ['config', 'list']).output.join('');
核心的一行代码的含义是什么?
1. 代码关键注解含义
// 注意:故意在 exec 上使用 spawn
// 否则问题不会重现。
// `npm config list` 是我能找到的唯一可靠的方法
// 重现错误的路径。只需打印 process.cwd()
// 在 Node 进程中是不够的
1. debug到具体执行后
如上childOutput:'; cli configs
2. 关键知识点补充
spawn
依赖的第三方库const spawn = require('cross-spawn');
spawn.sync
表示子进程异步执行命令
npm config list
可以直接在你的电脑控制台打印,实际上就是npm相关的一些配置,直接在控制台运行是同样的效果:
3. 继续执行
// `npm config list` 输出包括以下行:
// "; cwd = C:\path\to\current\dir" (未加引号)
// 我找不到更简单的方法来获取它。
lines
debug如下:
const prefix = '; cwd = ';
const line = lines.find(line => line.startsWith(prefix));
if (typeof line !== 'string') {
// Fail gracefully. They could remove it.
return true;
}
'; cwd = /create-react-app/packages/my-app'
判断不成立,继续向下执行;
4. npmCWD
if (npmCWD === cwd) {
return true;
}
成立返回true
;
函数执行完成