2.3.3 • Public • Published

    Electrum Events

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    The electrum-events module forwards web component events to the bus.

    Mouse capture utilities

    Capturing the mouse on Chrome (and electron) is tricky. electrum-events provides some helper functions to make the developer's life easier:

    • captureMouseEvents(e, listeners) captures the mouse until the mouse button gets released. The listeners object can specify functions onMouseMove(e) and onMouseUp(e) to process these events.
    • preventGlobalMouseEvents() and restoreGlobalMouseEvents() can be used to disable mouse events on a complete HTML document. This can come in handy if you want to make an HTML page passive.

    Note that captureMouseEvents() makes use of preventGlobalMouseEvents() so there is no need to call these functions when capturing the mouse events.

    The EventHandlers class

    The EventHandlers class provides implementations for the various event handlers needed by React web components:

    • handleBlur and handleFocus
    • handleChange
    • handleKeyDown, handleKeyUp and handleKeyPress
    • handleSelect

    Events are of two categories:

    • Events which modify a value (change, key up/down, select).
      They are sent with the bus.notify() function.
    • Events which trigger an action (focus, defocus, button click).
      They are sent with the bus.dispatch() function.

    Using EventHandlers

    Usually, you won't use EventHandlers yourself. It is Electrum's responsibility to inject the handlers into wrapped components. This is handled by Electrum's InjectingMiddleware:

    class Electrum {
      reset () {
        this._injectingMiddleware = new InjectingMiddleware ();
        this._injectingMiddleware.register ('events', obj => {
          obj._eventHandlers = EventHandlers.inject (obj, () => this.bus);

    The instance of the event handlers class attached to a component can be accessed through obj._eventHandlers. This might be useful when debugging (see below).

    EventHandlers properties

    Every event handlers instance provides the following public properties:

    • component → the component to which the handlers are attached.
    • props → the properties of the component.
    • bus → the bus to which the events will be sent.

    Debug with active logging

    Class EventHandlers has a property debug which can be set to log events to the console, which may prove convenient to better understand what happens.

    For customized logging, set debug to a function:

    const eh = new EventHandlers (obj, bus);
    eh.debug = (component, source, event) => { /* ... */ };

    The component argument refers to the component on which the event was notified. The source argument is one of focus, change, key-down, key-up, key-press and select, while the event argument gives full access to the event being processed.



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