The App State

App can be in one of the following three states:

• IDLE: The main function of the App is not running.
• UPDATE: Render the page.
• RECV: Receive an event.

The IDLE State

After the execution is finished in the UPDATE state, the App will enter the IDLE state.

The UPDATE State

There are three ways to enter the UPDATE state:

• Mount the App.
• Call the update method of the App.
• The event queue becomes empty.

In the UPDATE state, the App will render the DOM tree and update the page.

TIP

Multiple UPDATE calls will be merged into one.

DANGER

You SHOULD NOT change the state in the UPDATE state.

The following code is illegal, and may cause undefined behavior:

let count = 0;
$app([Basics], _ => {
  _.p(`Count is: ${count}`);
  count++; // The state will change in the UPDATE state
});

The RECV State

When an event is received, the App will enter the RECV state.

In this state, the return values of the trigger components can be true, if it is the event receiver.

After the execution is finished in the RECV state, the App will always enter the UPDATE state.

DANGER

You can't render the page in the RECV state.

The following code is illegal, and may cause undefined behavior:

$app([Basics], _ => {
  if (_.button("Click me")) {
    _.p("Hello");
  }
});