create nu_plugin_node_example.js (#15482)

example like
[nu_plugin_python_example.py](https://github.com/nushell/nushell/blob/main/crates/nu_plugin_python/nu_plugin_python_example.py)

crates/nu_plugin_javascript/nu_plugin_node_example.js

@@ -0,0 +1,248 @@
+#!/usr/bin/env node
+
+/**
+ * Node.js Nushell Plugin Example
+ * Communicates with Nushell via JSON-encoded messages over stdin/stdout
+ * 
+ * Register command: `plugin add -s 'C:\Program Files\nodejs\node.exe' ./nu_plugin_node_example.js`
+ * `plugin use ./nu_plugin_node_example.js`
+ * Usage: node_example 2 "3"
+ */
+
+// Configuration constants
+const NUSHELL_VERSION = '0.103.1';
+const PLUGIN_VERSION = '0.1.1';
+
+// Core protocol functions
+
+/**
+ * Writes a structured response to stdout
+ * @param {number} id - Call identifier
+ * @param {object} response - Response payload
+ */
+function writeResponse (id, response) {
+	const message = JSON.stringify({ CallResponse: [id, response] });
+	process.stdout.write(`${message}\n`);
+}
+
+/**
+ * Writes an error response
+ * @param {number} id - Call identifier
+ * @param {string} text - Error description
+ * @param {object|null} span - Error location metadata
+ */
+function writeError (id, text, span = null) {
+	const error = span ? {
+		Error: {
+			msg: 'Plugin execution error',
+			labels: [{ text, span }]
+		}
+	} : {
+		Error: {
+			msg: 'Plugin configuration error',
+			help: text
+		}
+	};
+	writeResponse(id, error);
+}
+
+// Plugin capability definitions
+
+/**
+ * Generates plugin signature metadata
+ * @returns {object} Structured plugin capabilities
+ */
+function getPluginSignature () {
+	return {
+		Signature: [{
+			sig: {
+				name: 'node_example',
+				description: 'Demonstration plugin for Node.js',
+				extra_description: '',
+				required_positional: [
+					{
+						name: 'a',
+						desc: 'Required integer parameter',
+						shape: 'Int'
+					},
+					{
+						name: 'b',
+						desc: 'Required string parameter',
+						shape: 'String'
+					}
+				],
+				optional_positional: [{
+					name: 'opt',
+					desc: 'Optional numeric parameter',
+					shape: 'Int'
+				}],
+				rest_positional: {
+					name: 'rest',
+					desc: 'Variable-length string parameters',
+					shape: 'String'
+				},
+				named: [
+					{
+						long: 'help',
+						short: 'h',
+						arg: null,
+						required: false,
+						desc: 'Display help information'
+					},
+					{
+						long: 'flag',
+						short: 'f',
+						arg: null,
+						required: false,
+						desc: 'Example boolean flag'
+					},
+					{
+						long: 'named',
+						short: 'n',
+						arg: 'String',
+						required: false,
+						desc: 'Example named parameter'
+					}
+				],
+				input_output_types: [['Any', 'Any']],
+				allow_variants_without_examples: true,
+				search_terms: ['nodejs', 'example'],
+				is_filter: false,
+				creates_scope: false,
+				allows_unknown_args: false,
+				category: 'Experimental'
+			},
+			examples: []
+		}]
+	};
+}
+
+/**
+ * Processes execution calls from Nushell
+ * @param {number} id - Call identifier
+ * @param {object} callData - Execution context metadata
+ */
+function processExecutionCall (id, callData) {
+	const span = callData.call.head;
+
+	// Generate sample tabular data
+	const tableData = Array.from({ length: 10 }, (_, index) => ({
+		Record: {
+			val: {
+				one: { Int: { val: index * 1, span } },
+				two: { Int: { val: index * 2, span } },
+				three: { Int: { val: index * 3, span } }
+			},
+			span
+		}
+	}));
+
+	writeResponse(id, {
+		PipelineData: {
+			Value: [{
+				List: {
+					vals: tableData,
+					span
+				}
+			}, null]
+		}
+	});
+}
+
+// Protocol handling
+
+/**
+ * Handles different types of input messages
+ * @param {object} input - Parsed JSON message from Nushell
+ */
+function handleInputMessage (input) {
+	if (input.Hello) {
+		handleHelloMessage(input.Hello);
+	} else if (input === 'Goodbye') {
+		process.exit(0);
+	} else if (input.Call) {
+		handleCallMessage(...input.Call);
+	} else if (input.Signal) {
+		handleSignal(input.Signal);
+	}
+}
+
+function handleHelloMessage ({ version }) {
+	if (version !== NUSHELL_VERSION) {
+		process.stderr.write(`Version mismatch: Expected ${NUSHELL_VERSION}, got ${version}\n`);
+		process.exit(1);
+	}
+}
+
+function handleCallMessage (id, call) {
+	try {
+		if (call === 'Metadata') {
+			writeResponse(id, { Metadata: { version: PLUGIN_VERSION } });
+		} else if (call === 'Signature') {
+			writeResponse(id, getPluginSignature());
+		} else if (call.Run) {
+			processExecutionCall(id, call.Run);
+		} else {
+			writeError(id, `Unsupported operation: ${JSON.stringify(call)}`);
+		}
+	} catch (error) {
+		writeError(id, `Processing error: ${error.message}`);
+	}
+}
+
+function handleSignal (signal) {
+	if (signal !== 'Reset') {
+		process.stderr.write(`Unhandled signal: ${signal}\n`);
+	}
+}
+
+// Stream processing setup
+
+/**
+ * Initializes plugin communication protocol
+ */
+function initializePlugin () {
+	// Set up JSON encoding
+	process.stdout.write('\x04json\n');
+
+	// Send handshake message
+	process.stdout.write(JSON.stringify({
+		Hello: {
+			protocol: 'nu-plugin',
+			version: NUSHELL_VERSION,
+			features: []
+		}
+	}) + '\n');
+
+	// Configure input processing
+	let buffer = '';
+	process.stdin.setEncoding('utf8')
+		.on('data', chunk => {
+			buffer += chunk;
+			const messages = buffer.split('\n');
+			buffer = messages.pop() || ''; // Preserve incomplete line
+
+			for (const message of messages) {
+				if (message.trim()) {
+					try {
+						handleInputMessage(JSON.parse(message));
+					} catch (error) {
+						process.stderr.write(`Parse error: ${error.message}\n`);
+						process.stderr.write(`Received: ${message}\n`);
+					}
+				}
+			}
+		})
+		.on('error', error => {
+			process.stderr.write(`Input error: ${error.message}\n`);
+			process.exit(1);
+		});
+}
+
+// Main execution
+if (process.argv.includes('--stdio')) {
+	initializePlugin();
+} else {
+	console.log('This plugin is intended to be run from within Nushell');
+	process.exit(2);
+}