num width

The width of this rectangle.

This is equivalent to the width function in jQuery and the calculated width CSS value, converted to a dimensionless num in pixels. Unlike getBoundingClientRect, width will return the same numerical width if the element is hidden or not.

Source 

num get width;
void width=(newWidth)

Set the current computed width in pixels of this element.

newWidth can be either a num representing the width in pixels or a Dimension object. This is equivalent to the width function in jQuery and the calculated width CSS value, converted to a dimensionless num in pixels.

Note that only the content width can be set via this method.

Source 

set width(newWidth) {
  throw new UnsupportedError("Can only set width for content rect.");
}