Why Does Simulating Mouseover in JavaScript Fail to Activate CSS \":hover\"?

Simulating Mouseover in JavaScript: Why CSS ":hover" Remains Inactive

Simulating mouseover events in JavaScript presents a unique challenge: activating the ":hover" CSS declaration. Despite the triggering of the "mouseover" listener, the CSS hover effect fails to display. This article delves into the reason behind this behavior and offers an alternative solution.

The Trusted Event Conundrum

According to the HTML specification, certain events are classified as "trusted," granting them special privileges that untrusted events, generated by JavaScript, lack. Untrusted events, such as those simulated via the DocumentEvent.createEvent() or dispatched through EventTarget.dispatchEvent(), cannot trigger default actions, including CSS hover effects.

This limitation stems from security concerns to prevent malicious scripts from executing arbitrary actions. By barring untrusted events from performing default actions, the browser ensures user protection.

Alternative Solution: Manual Class Manipulation

Since simulating mouseover events directly to activate ":hover" is not feasible, an alternative approach involves manually manipulating the element's class. Utilize the mouseover/mouseout events to add or remove a custom class that mirrors the desired hover effect. For instance:

<code class="javascript">const element = document.querySelector('#my-element');

element.addEventListener('mouseover', () => {
  element.classList.add('hover');
});

element.addEventListener('mouseout', () => {
  element.classList.remove('hover');
});</code>

By employing this technique, you can simulate mouseover behavior and achieve the desired hover effects, albeit through a manual class manipulation process.

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