perf: Remove obsolete IE8 computedStyle fallback in getBoundingClientRect wrapper

[PascalThuet]

Description

The getBoundingClientRect() wrapper in dom.js includes a fallback that calls computedStyle() when height or width are missing from the native getBoundingClientRect() result. This fallback was added for IE8 compatibility, which is no longer supported.

Current Code (dom.js:456-477)

export function getBoundingClientRect(el) {
  if (el && el.getBoundingClientRect && el.parentNode) {
    const rect = el.getBoundingClientRect();
    const result = {};

    ['bottom', 'height', 'left', 'right', 'top', 'width'].forEach(k => {
      if (rect[k] !== undefined) {
        result[k] = rect[k];
      }
    });

    // IE8 fallback - no longer needed
    if (!result.height) {
      result.height = parseFloat(computedStyle(el, 'height'));
    }
    if (!result.width) {
      result.width = parseFloat(computedStyle(el, 'width'));
    }

    return result;
  }
}

Proposed Fix

Simplify to direct property access (all modern browsers provide these properties):

export function getBoundingClientRect(el) {
  if (el && el.getBoundingClientRect && el.parentNode) {
    const rect = el.getBoundingClientRect();
    return {
      bottom: rect.bottom,
      height: rect.height,
      left: rect.left,
      right: rect.right,
      top: rect.top,
      width: rect.width
    };
  }
}

Benchmark Results

Metric	Current	Optimized	Improvement
10,000 calls	15.90 ms	3.20 ms	80% faster
Per call	1.59 µs	0.32 µs	-1.27 µs

Impact

This function is called frequently during:

• Seek bar scrubbing: ~30 times/second via getPointerPosition()
• Volume control interaction
• Tooltip positioning

On mobile devices (4x slower JS execution), this translates to ~5ms/sec savings during scrubbing.

Browser Support

All browsers currently supported by video.js provide height and width from getBoundingClientRect():

• Chrome 1+
• Firefox 3+
• Safari 4+
• Edge (all versions)

IE8 support was dropped years ago.

Environment

• video.js version: 8.23.6
• Tested on: Chrome 144, macOS

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[mister-ben]

Perhaps just return rect?

[PascalThuet]

Good point! I checked all call sites in the codebase — seek-bar.js, time-tooltip.js, volume-bar.js, volume-level-tooltip.js — and none of them mutate the returned object; they only read properties (.width, .left, .right, etc.).

The original JSDoc mentioned shallow-copying to avoid non-enumerable keys on DOMRect, but since no code iterates over the keys (no Object.keys() or for...in on the result), that's not a concern in practice.

I'll simplify to just return el.getBoundingClientRect() and update the existing unit test in dom.test.js which explicitly asserts the result is cloned. I'll also update the JSDoc accordingly.