✨hide or not to hide?
browser ⟩ event ⟩ default action ⟩ example ⟩ hide or not to hide?
function
💾 replit
const {log} = console;
// ⭐️ import
import {$} from './js/Node+ext.js';
// -------------------------------------------
// elements
const rabbit = $('#rabbit');
const button = $('button');
// scenario A
// -------------------------------------------------------------
// 1. click the button
//
// 2. confirm dialog ("rabbit.onhide")
// (confirm dialog shows BEFORE the log message, why❓)
//
// 3. click "OK"
//
// 4. dispatching "hide" event on rabbit ... ("button.onclick")
// (this message shows AFTER the confirm dialog, why❓)
//
// 5. default action prevented ... ("rabbit.onhide")
// 6. "hide" event on rabbit dispatched ... ("button.onclick")
// 7. "hiding rabbit" cancelled ... ("button.onclick")
//
// scenario A
// -------------------------------------------------------------
// 1. click the button
// 2. confirm dialog ("rabbit.onhide")
// 3. click "Cancel"
// 4. dispatching "hide" event on rabbit ... ("button.onclick")
// 5. "hide" event on rabbit dispatched ... ("button.onclick")
// button.onclick
button.onclick = () => {
// ⭐️ cancelable custom "hide" event
let hideEvent = new CustomEvent("hide", {
cancelable: true // ⭐️ preventDefault doesn't work without this
});
// start to dispatch hide event
log(`dispatching "hide" event on rabbit ...`);
// ⭐️ dispatch 'hide' on rabbit and see if the event handler
// decides to do the default actions or not.
let doDefaults = rabbit.dispatchEvent(hideEvent);
log(`"hide" event on rabbit dispatched ...`);
if (!doDefaults) {
log('"hiding rabbit" cancelled ...');
return;
}
// hide the rabbit
rabbit.hidden = true;
};
// rabbit.onhide
rabbit.addEventListener('hide', (event) => {
if (confirm("Cancel hidding?")) {
// By calling event.preventDefault(), an event handler
// may send a signal to cancel default actions.
// ⭐️ In this case, elem.dispatchEvent(event) returns false❗️
// "Don't do default actions."
event.preventDefault();
log('default action prevented ...');
}
});
return value of EventTarget ⟩ .dispatchEvent(event)
false
if
event
is cancelable, andat least one of the event's handlers called .preventDefault().
true, otherwise.
the return value of an event handler is related to canceling the default actions.
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