In this chapter, we're going to learn how to make commands.

Making a command

A command is an execution unit that can be called by menu item, keyboard shortcuts or any parts of applications via API. All menu items such as File > Open..., Edit > Copy have corresponding commands. So you must make a command first before to add a menu item. As shown in Getting Started, we will make a simple command showing a message in alert dialog.

First you have to defined an unique ID for a command. Typical command ID have the form <group>:<function> where <group> is the group name of commands and <function> is the function name of the command. An extension may have a set of commands, so typically the group name is the extension name. For example, the ID of the command showing a message of HelloWorld extension is helloworld:show-message.

And then, we will define a handler function to be executed when the command is called.

function handleShowMessage() {
window.alert('Hello, world!')

Finally, we need to register this command to application by calling app.commands.register method. The first parameter is the ID of the command and the second is the handler function and the third (optional) is the display name of the command (Shown in Command Palette).

app.commands.register('helloworld:show-message', handleShowMessage, 'Show Message')

Calling a command

Now we have a new helloworld:show-message command. It can be called manually as follow:


All functionalities of StarUML are defined as commands so that you can call without defining duplicated functionality.

var ids = Object.keys(app.commands.commands)
console.log(ids); // you can see all available command IDs
app.commands.execute('project:open') // execute `project:open` command

Passing parameters

You can pass one or more parameters to the command. We will fix the handle function so that it can receive a parameter (two or more parameters are possible).

function handleShowMessage(message) {
if (message) {
} else {
window.alert('Hello, world!')

Then, you can pass a string to the parameter as follow:

app.commands.execute('helloworld:show-message', 'New Message')