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Using TypeScript for Building Polymorphic React Components

Handling Default Values for the Polymorphic Prop

Learn to pass a default generic value and leverage that in a polymorphic component.

We'll cover the following...

Let's consider our current solution, and pay attention to where a default element is provided if the as prop is omitted.

TypeScript 3.3.4
type PolymorphicTextProps<C extends React.ElementType> = {
  as?: C;
  children: React.ReactNode;
} & React.ComponentPropsWithoutRef<C>; 
export const PolymorphicText = <C extends React.ElementType>({
  as,
  children,
  ...restProps
}: PolymorphicTextProps<C>) => {
  const Component = as || "span";
  return <Component {...restProps}>{children}</Component>;
};

Let's look at line 11 above. If the as prop is not provided, it will default to the string span.

Default JavaScript values

The ...