@navikt/ds-react/src/slot/merge-props.ts

React components from the Norwegian Labour and Welfare Administration.

function mergeProps(
  slotProps: Record<string, any>,
  childProps: Record<string, any>,
) {
  // all child props should override
  const overrideProps = { ...childProps };

  for (const propName in childProps) {
    const slotPropValue = slotProps[propName];
    const childPropValue = childProps[propName];

    const isHandler = /^on[A-Z]/.test(propName);
    if (isHandler) {
      // if the handler exists on both, we compose them
      if (slotPropValue && childPropValue) {
        overrideProps[propName] = (...args: unknown[]) => {
          childPropValue(...args);
          slotPropValue(...args);
        };
      }
      // but if it exists only on the slot, we use only this one
      else if (slotPropValue) {
        overrideProps[propName] = slotPropValue;
      }
    }
    // if it's `style`, we merge them
    else if (propName === "style") {
      overrideProps[propName] = { ...slotPropValue, ...childPropValue };
    } else if (propName === "className") {
      overrideProps[propName] = [slotPropValue, childPropValue]
        .filter(Boolean)
        .join(" ");
    }
  }

  return { ...slotProps, ...overrideProps };
}

export { mergeProps };