Mouse Events in JavaScript: Why Your UI Flickers (and How to Fix It Properly)

Source: Dev.to

Hover interactions feel simple—until they quietly break your UI.

Recently, while building a data table, each row had an “Actions” column that appears on hover. Most of the time it worked, but when moving the mouse slowly or crossing row borders the UI flickered, and sometimes two rows showed actions simultaneously. The culprit wasn’t CSS or rendering; it was the mouse‑event model.

The Two Families of Mouse Hover Events

The distinction between bubbling and non‑bubbling hover events is one of the most important in UI engineering.

Why mouseover Is Dangerous for UI State

<tr>
  <td>Name</td>
  <td>
    <button>Edit</button>
    <button>Delete</button>
  </td>
</tr>

From the user’s perspective they are still “hovering the row” when moving between the buttons. From the browser’s perspective the pointer traverses:

→  →

Each transition fires new mouseover and mouseout events as the cursor moves through child elements. Consequently:

• Moving from one button to another fires mouseout on the first button, which bubbles up.
• The row receives a “mouse left” signal even though the user never left the row.

This mismatch between DOM movement and human intent causes flicker.

How My Table Broke

• Each row displayed action buttons on hover.
• A 1 px border existed between rows.
• When the cursor crossed that border, it briefly exited one row before entering the next.

Resulting sequence:

1. mouseout → hide actions on the first row.
2. mouseover → show actions on the next row.

If the timing was fast enough, two rows appeared active simultaneously, producing a flicker. The layout was fine; the event model was simply misrepresenting user intent.

Why mouseenter Solves This

mouseenter and mouseleave do not bubble and fire only when the pointer actually enters or leaves the element itself—not its children. The same movement:

→  →

Triggers only a single mouseenter(tr) (and later a single mouseleave(tr)), eliminating false exits and preventing flicker. This makes them ideal for:

• Table rows
• Dropdown menus
• Tooltips
• Hover cards
• Any UI that should stay active while the cursor remains inside the element

In short:

• mouseenter → user intent
• mouseover → DOM traversal

When You Should Use Each

Use mouseenter / mouseleave when:

• You are toggling UI state based on hover.
• Child elements should not interrupt the hover.
• Stability matters.

Examples

• Row actions
• Navigation menus
• Profile cards
• Tooltips

Use mouseover / mouseout when:

• You need to know which child element was entered or left.
• Bubbling is useful for delegating behavior.

Examples

• Image maps
• Per‑icon tooltips
• Custom hover effects on individual elements

React Makes This More Subtle

In React, onMouseOver and onMouseOut are wrapped in a synthetic event system, adding another layer of propagation and re‑rendering. This can amplify flicker and race conditions, making hover‑driven UIs harder to get right.

A Practical Rule of Thumb

If you are using mouseover to control UI visibility, you are likely building something fragile. Most hover‑based interfaces should be built with mouseenter / mouseleave because users hover things, not raw DOM nodes.

Final Thoughts

The small flicker in my table wasn’t a bug—it was a reminder of how deep the browser’s event model really is. The best UI engineers write logic that matches how humans actually interact with the screen. Often, the difference between a glitchy UI and a rock‑solid one is just a single event name.