ResizeObserverSize: blockSize property

{{APIRef("Resize Observer API")}}

The blockSize read-only property of the {{domxref("ResizeObserverSize")}} interface returns the length of the observed element's border box in the block dimension. For boxes with a horizontal {{cssxref("writing-mode")}}, this is the vertical dimension, or height; if the writing-mode is vertical, this is the horizontal dimension, or width.

[!NOTE] For more explanation of writing modes and block and inline dimensions, read Handling different text directions.

Value

A decimal representing the block size in pixels.

Examples

In this example we return an array of sizing information with {{domxref("ResizeObserverEntry.contentBoxSize")}}. The blockSize property returns the block dimension size of the observed element.

const resizeObserver = new ResizeObserver((entries) => {
  for (const entry of entries) {
    const elemSize = entry.contentBoxSize[0];
    console.log(elemSize.blockSize); // a decimal
  }
});

resizeObserver.observe(divElem);

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}