Skip to content

AppRun Dev Tools

We have been using the command-line interface (CLI) in the terminal window and the command prompt. Have you thought of a CLI in the console of the browser's developer tool?

AppRun Dev Tools

How does it work?

In the console of the browser's developer tool (F12), you can type the command.

_apprun `<command> [options]`

Just like many other CLI, the help command lists all available commands. For example, you can see three commands in the screenshotcomponents, events, and log.

Why do we need a CLI in the console?

CLI in the console is convenient for watching runtime data. For example, during application development, we often need to debug and check the application's internal data. Using the console.log function is the easiest yet most compelling way to display the data because the console lets us drill down into the nested array and object structure.


With a CLI in the console, The app codebase stays clear of console.log. The CLI provides a non-destructive way of watching the runtime data. We can include the CLI script in the development environment and remove it from the production environment.

How is it made?

The CLI uses JavaScript tagged templates.

We create the _apprun function in the window object.

window['_apprun'] = (strings) => { }

The _apprun function is called when we type the AppRun commands in the console. The command and the command parameters are passed into the _apprun function as the function parameter strings, which we can parse and then invoke the command functions.

window['_apprun'] = (strings) => {
  const [cmd, ...p] = strings[0].split(' ').filter(c => !!c);
  const command = window[`_apprun-${cmd}`];
  if (command) command[1](...p);
  else window['_apprun-help'][1]();
It has extensive architecture. We create the AppRun commands in the window object. The AppRun command is a tuple that includes the description of the command and the implementation function of the command. E.g., the help command looks like this:

window['_apprun-help'] = ['', () => {
  Object.keys(window).forEach(cmd => {
    if (cmd.startsWith('_apprun-')) {
      cmd === '_apprun-help' ?
        console.log('AppRun Commands:') :
        console.log(`* ${cmd.substring(8)}: ${window[cmd][0]}`);
The help command searches for the tuples stored in the window object and prints the description of other AppRun commands.

That's all the infrastructure code we need to create CLI commands in the console. Let's see an example.

Live Demo

The AppRun Dev Tools is one of the developer tools included in the AppRun library. You can visit the AppRun RealWorld Example App to see the CLI in action.

  • The components command logs the DOM elements that have AppRun components
  • The events command logs the event subscription of the app
  • The log command logs the runtime events publication of the app
  • The create-event-tests command creates unit tests for the app
  • The create-state-tests command creates Jest snapshot tests for the app


Developers like CLI. Dev Tools helps get runtime events and messages hard for the traditional CLI in the terminal. The AppRun Dev Tools can watch the components and events, and can generate tests. Thus, it increases the development productivity for debugging and testing.