Використання датчиків та подій пристрою в JavaScript для інтерактивних веб-додатків

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Використання датчиків та подій пристрою в JavaScript для інтерактивних веб-додатків image

Питання-відповіді

What are event listeners in JavaScript?

Event listeners in JavaScript are functions that wait for a specific event to occur on a particular element, like a click or a mouseover event. Once the event occurs, the listener triggers a callback function to execute some tasks.

How do you add an event listener to an HTML element?

You can add an event listener to an HTML element using the `addEventListener` method in JavaScript. This method takes two arguments: the event you want to listen for (e.g., ‘click’) and the callback function you want to execute when the event occurs.

What is the difference between onclick and addEventListener?

The `onclick` attribute is an older way of attaching event handlers directly to HTML elements in a specific tag. On the other hand, `addEventListener` is a more modern approach that allows you to add multiple event listeners to the same element and provides more flexibility.

How can you remove an event listener?

You can remove an event listener using the `removeEventListener` method in JavaScript. This method takes the same arguments as `addEventListener` (i.e., the event type and the callback function) to correctly identify and remove the listener.

What is event bubbling in JavaScript?

Event bubbling is a phase in the event propagation model where the event first triggers on the target element and then “bubbles up” through its ancestors in the DOM tree. This allows you to handle events at different levels of the DOM hierarchy.

What is event delegation?

Event delegation is a technique in JavaScript where you attach a single event listener to a common ancestor of multiple elements instead of attaching listeners to each individual element. This can improve performance and simplify event handling in complex DOM structures.

How do you prevent the default behavior of an event?

You can prevent the default behavior of an event in JavaScript by calling the `preventDefault` method on the event object. This stops the browser from executing the default action associated with the event, such as following a link or submitting a form.

What is the difference between capturing and bubbling phases in event propagation?

Event propagation in JavaScript consists of two phases: capturing phase and bubbling phase. In the capturing phase, events are triggered from the top of the DOM hierarchy down to the target element, while in the bubbling phase, events bubble up from the target element to the top of the hierarchy.

How can you check which element triggered an event?

You can check which element triggered an event by accessing the `target` property of the event object in JavaScript. This property refers to the element that actually triggered the event, even if the event bubbled up through multiple ancestors.

Can you have multiple event listeners for the same event on a single element?

Yes, you can have multiple event listeners for the same event on a single element in JavaScript. By using `addEventListener` with different callback functions, you can attach several handlers to an element to perform different actions when the event occurs.
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Основи JavaScript Обробка подій та AJAX запити
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