fix(Handler): allow click through when elements are recreated between mousedown and mouseup

[waterWang]

Summary

When setOption is called at high frequency (>=30fps, e.g. real-time WebSocket data) between mousedown and mouseup, zrender elements are recreated. The click handler compares element references (_downEl !== _upEl), which always fails for recreated elements, causing click events (e.g. legend toggle) to never fire.

This bug is reported as apache/echarts#21566.

Root Cause

In Handler.ts, the click handler checks:

if (this._downEl !== this._upEl) { return; }

When setOption is called between mousedown and mouseup, the display list is updated and elements are recreated. The _downEl reference (stored during mousedown) points to the old, removed element, while _upEl (set during mouseup) points to the new element. The reference comparison always fails, cancelling all click events.

Fix

Use the existing __zr check pattern (already used in the mousemove handler at line ~424) to detect when _downEl was removed from zrender due to element recreation. If the element was removed (i.e., _downEl.__zr is falsy), allow the click to proceed to the new element at the same position.

The mousemove handler already uses this pattern:

if (lastHoveredTarget && !lastHoveredTarget.__zr) {
    lastHovered = this.findHover(lastHovered.x, lastHovered.y);
}

Testing

• Clicking legend items works correctly when setOption is called at 60fps
• Dragging (pan/zoom) is unaffected — the mousemove distance check (> 4px) still applies
• Normal click behavior is preserved when elements are not recreated