helloworld-web-sample/src/web/extension.ts

// The module 'vscode' contains the VS Code extensibility API
// Import the module and reference it with the alias vscode in your code below
import * as vscode from 'vscode';

// This method is called when your extension is activated
// your extension is activated the very first time the command is executed
export function activate(context: vscode.ExtensionContext) {

	// Use the console to output diagnostic information (console.log) and errors (console.error)
	// This line of code will only be executed once when your extension is activated
	console.log('Congratulations, your extension "helloworld-web-sample" is now active in the web extension host!');

	// The command has been defined in the package.json file
	// Now provide the implementation of the command with registerCommand
	// The commandId parameter must match the command field in package.json
	const disposable = vscode.commands.registerCommand('helloworld-web-sample.helloWorld', () => {
		// The code you place here will be executed every time your command is executed

		// Display a message box to the user
		vscode.window.showInformationMessage('Hello World from helloworld-web-sample in a web extension host!');
	});

	context.subscriptions.push(disposable);
}

// This method is called when your extension is deactivated
export function deactivate() {
	// Noop
}