implement dev command

scripts/dev.js

@@ -0,0 +1,36 @@
+const execa = require('execa');
+
+(async () => {
+	execa('npx', ['gulp', 'watch'], {
+		cwd: __dirname + '/../',
+		stdout: process.stdout,
+		stderr: process.stderr,
+	});
+
+	execa('npm', ['run', 'watch'], {
+		cwd: __dirname + '/../packages/backend',
+		stdout: process.stdout,
+		stderr: process.stderr,
+	});
+
+	execa('npm', ['run', 'watch'], {
+		cwd: __dirname + '/../packages/client',
+		stdout: process.stdout,
+		stderr: process.stderr,
+	});
+
+	const start = async () => {
+		try {
+			await execa('npm', ['run', 'start'], {
+				cwd: __dirname + '/../',
+				stdout: process.stdout,
+				stderr: process.stderr,
+			});
+		} catch (e) {
+			await new Promise(resolve => setTimeout(resolve, 3000));
+			start();
+		}
+	};
+
+	start();
+})();