npm and error messages

node_modules/laravel-mix/src/Dependencies.js

@@ -0,0 +1,56 @@
+let process = require('child_process');
+let File = require('../src/File');
+
+class Dependencies {
+    constructor(dependencies) {
+        this.dependencies = dependencies;
+    }
+
+    install(abortOnComplete = false) {
+        this.dependencies
+            .reject(dependency => {
+                try {
+                    return require.resolve(
+                        dependency.replace(/(?!^@)@.+$/, '')
+                    );
+                } catch (e) {}
+            })
+            .tap(dependencies => {
+                this.execute(
+                    this.buildInstallCommand(dependencies),
+                    abortOnComplete
+                );
+            });
+    }
+
+    execute(command, abortOnComplete) {
+        console.log(
+            'Additional dependencies must be installed. ' +
+                'This will only take a moment.'
+        );
+
+        process.execSync(command);
+
+        if (abortOnComplete) {
+            console.log(
+                typeof abortOnComplete === 'string'
+                    ? abortOnComplete
+                    : 'Finished. Please run Mix again.'
+            );
+
+            process.exit();
+        }
+    }
+
+    buildInstallCommand(dependencies) {
+        dependencies = [].concat(dependencies).join(' ');
+
+        if (File.exists('yarn.lock')) {
+            return `yarn add ${dependencies} --dev`;
+        }
+
+        return `npm install ${dependencies} --save-dev`;
+    }
+}
+
+module.exports = Dependencies;