Function composeCaretRect

composeCaretRect(
    p: {
        markerRect: { height: number; left: number; top: number };
        mirrorRect: { left: number; top: number };
        scrollLeft: number;
        scrollTop: number;
        textareaRect: { left: number; top: number };
    },
): CaretRect
Compose the viewport-space caret rect from the three measured boxes — the pure core of the caret geometry, split out so it can be unit-tested without a layout engine (jsdom does no layout).

The caret's offset within the content is marker.left/top − mirror.left/top: because the mirror copies the textarea's border + padding, that delta measured from the mirror's border-box corner equals the same offset from the textarea's border-box corner. Add the textarea's viewport position and subtract its scroll to land on the on-screen caret.
Parameters
- p: {
      markerRect: { height: number; left: number; top: number };
      mirrorRect: { left: number; top: number };
      scrollLeft: number;
      scrollTop: number;
      textareaRect: { left: number; top: number };
  }
  - markerRect: { height: number; left: number; top: number }
    
    The caret marker span's box: origin (viewport space) + its line-box height (the caret height).
  - mirrorRect: { left: number; top: number }
    
    The mirror's border-box origin, viewport space.
  - scrollLeft: number
    
    textarea.scrollLeft — the caret shifts left as the field scrolls right.
  - scrollTop: number
    
    textarea.scrollTop.
  - textareaRect: { left: number; top: number }
    
    The textarea's border-box origin, viewport space (textarea.getBoundingClientRect()).
Returns CaretRect

Function composeCaretRect

Parameters

markerRect: { height: number; left: number; top: number }

mirrorRect: { left: number; top: number }

scrollLeft: number

scrollTop: number

textareaRect: { left: number; top: number }

Returns CaretRect

Settings