🍄object handler

JS ⟩ browser ⟩ event ⟩ handler ⟩ register ⟩ object handler

delegate event handling to an object：

elem.addEventListener('click', {
    // calls handleEvent(event) in case of an event.
    handleEvent(event) { ... }    // ⭐️ required method
});

⭐️ 重點

could also use a class instance for that:

class Menu {
    // ⭐️ required method
    handleEvent(event) {
      switch(event.type) {
        case 'mousedown': ...; break;
        case 'mouseup'  : ...; break;
      }
    }
    // other methods/properties ...
}

// Menu can also be written like this:
class Menu {

    // ⭐️ required method
    handleEvent(event) {
      const methodName = "on" + event.type;  // onmousedown, onmouseup ...
      this[methodName] ?. (event);           // optional invocation
    }
    
    // methods for individual event
    onmousedown(event){ ... }
    onmouseup  (event){ ... }
}

let menu = new Menu();    // object handler

elem.addEventListener('mousedown', menu);
elem.addEventListener('mouseup'  , menu);

👥 相關

• optional invocation ?.()

📗 參考

• JS.info ⟩ object handlers