The CSSUnitValue.unit read-only property of the CSSUnitValue interface returns a string indicating the type of unit.

A string.

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

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

console.log(pos.x.unit); // "px"
console.log(pos.y.unit); // "em"

• CSSUnitValue.value
• Dimensions in CSS units and values
• Using the CSS Typed OM
• CSS Typed Object Model API