关于webpack4:寻找webpack打包入口

node_modules下.bin目录下有一个webpack.cmd脚本文件，组装定位了要执行的webpack.js文件

"%~dp0\node.exe"  "%~dp0\..\webpack\bin\webpack.js" %*

将启动文件指向了webpack目录下的bin\webpack.js。

在webpack.js文件中，有一个runCommond办法和isInstalled判断包是否装置函数,

const runCommand = (command, args) => {
    const cp = require("child_process");
    return new Promise((resolve, reject) => {
        const executedCommand = cp.spawn(command, args, {
            stdio: "inherit",
            shell: true
        });

        executedCommand.on("error", error => {
            reject(error);
        });

        executedCommand.on("exit", code => {
            if (code === 0) {
                resolve();
            } else {
                reject();
            }
        });
    });
};
const isInstalled = packageName => {
    try {
        require.resolve(packageName);

        return true;
    } catch (err) {
        return false;
    }
};

installedClis获取曾经装置的cli，这外面重要的就是CLIs数组中第一行isInstalled("webpack-cli"),指向了webpack-cli。

const installedClis = CLIs.filter(cli => cli.installed);

接下来依据filter办法找到曾经安装包，解决了包门路，通过最初的require导入了wbpack-cli/bin/cli.js

    const path = require("path");
    const pkgPath = require.resolve(`${installedClis[0].package}/package.json`);
    // eslint-disable-next-line node/no-missing-require
    const pkg = require(pkgPath);
    // eslint-disable-next-line node/no-missing-require
    require(path.resolve(
        path.dirname(pkgPath),
        pkg.bin[installedClis[0].binName]
    ));

在wbpack-cli/bin/cli.js中，是一个IIFE,个别的cli文件中个别有二个操作，解决参数，将参数交给不同的逻辑（散发业务），文件中导入webpack，创立一个webpack实例。依据参数options创立一个compile实例，挂载钩子，

    const webpack = require("webpack");

    let lastHash = null;
    let compiler;
    try {
    compiler = webpack(options);
    } catch (err) {
    if (err.name === "WebpackOptionsValidationError") {
        if (argv.color) console.error(`\u001b[1m\u001b[31m${err.message}\u001b[39m\u001b[22m`);
        else console.error(err.message);
        // eslint-disable-next-line no-process-exit
        process.exit(1);
    }

    throw err;
    }

在文件结尾处，就找到了webpack打包入口run办法

compiler.run((err, stats) => {
    if (compiler.close) {
        compiler.close(err2 => {
            compilerCallback(err || err2, stats);
        });
    } else {
        compilerCallback(err, stats);
    }
});