webpack检测webpack cli是否安装的方法

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const isInstalled = packageName => {     if (process.versions.pnp) {         return true;     }       const path = require("path");     const fs = require("graceful-fs");       let dir = __dirname;       do {         try {             if (                 fs.statSync(path.join(dir, "node_modules", packageName)).isDirectory()             ) {                 return true;             }         } catch (_error) {             // Nothing         }     } while (dir !== (dir = path.dirname(dir)));       return false; };

　　通过do while循环，往上面一层层的查找