You are correct; the MouseEvent.movementX and MouseEvent.movementY properties can behave differently across different browsers. These properties are part of the Pointer Events API, and the variation in their behavior is due to browser implementations and standards compliance.

Here's a summary of the differences you might encounter in different browsers:

  1. Chrome and Edge:

    • Both Chrome and Edge support the movementX and movementY properties for mouse events.
    • These properties provide the distance, in pixels, that the pointer (mouse) has moved horizontally and vertically since the last mouse event.
    • Positive movementX values indicate movement to the right, and negative values indicate movement to the left. Positive movementY values indicate movement downwards, and negative values indicate movement upwards.
  2. Firefox:

    • Firefox supports the movementX and movementY properties, but there are some differences compared to Chrome and Edge.
    • In Firefox, the movementX and movementY properties are only available for mouse events that are generated by a real mouse movement. These properties are not provided for synthetic mouse events (e.g., mouse events triggered by JavaScript).
    • Firefox follows the same convention for the direction of movement (positive and negative values) as Chrome and Edge.

To maintain cross-browser compatibility, you can use the following approach:

function getMouseMovement(event) { let movementX, movementY; if (event.movementX !== undefined && event.movementY !== undefined) { // For Chrome and Edge movementX = event.movementX; movementY = event.movementY; } else { // For Firefox or other browsers (e.g., Safari) // Calculate the movement by comparing the current event's clientX and clientY with the previous event's clientX and clientY. // Store the previous clientX and clientY in a closure or a variable accessible in your code. // Example: movementX = event.clientX - prevClientX; movementY = event.clientY - prevClientY; } // Update the previous clientX and clientY values for the next event. prevClientX = event.clientX; prevClientY = event.clientY; return { movementX, movementY }; }

By using this approach, you can handle both Chrome/Edge (where movementX and movementY are available) and Firefox (where you calculate the movement manually) correctly, ensuring consistent behavior across different browsers.

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