The CSSUnitValue.value property of the CSSUnitValue interface returns a double indicating the number of units.

A double.

The following creates a CSSPositionValue from individual CSSUnitValue constructors, then queries the CSSUnitValue.value.

const pos = new CSSPositionValue(
  new CSSUnitValue(5, "px"),
  new CSSUnitValue(10, "px"),
);

console.log(pos.x.value); // 5
console.log(pos.y.value); // 10

• CSSUnitValue.unit
• Using the CSS Typed OM
• CSS Typed Object Model API