Salesforce JavaScript Developer Practice Exam

What happens if an event listener is added to a parent div instead of an inner div?

1. The event listener cannot be triggered

2. The inner div’s listener will be ignored

3. Events bubble up to the parent element

4. It causes a runtime error

The correct answer is: Events bubble up to the parent element

When an event listener is added to a parent div instead of an inner div, the correct assertion is that events bubble up to the parent element. This phenomenon is known as event bubbling in the DOM (Document Object Model). When an event occurs on an element, the event first triggers on the target element, and then it propagates upward through its ancestors (parent elements) in the DOM tree. Therefore, if an event listener is added to a parent div, it will respond to events that occur on its children, including any inner divs. This allows for a more efficient handling of events since you can add fewer event listeners on parent elements instead of individual listeners on each child element, thus reducing memory usage and improving performance. In this context, options that suggest the event listener cannot be triggered or that the inner div’s listener will be ignored incorrectly imply limitations that do not occur with event bubbling. Additionally, claiming that it causes a runtime error is inaccurate, as adding an event listener normally does not produce errors under standard circumstances. The nature of event propagation is key to understanding how event listeners interact with nested elements in the DOM.