How to check the type of function parameters?

Question

typescript

Type for object methods - AuthFormsType

type AuthFormsType = {
  [s:string] : (props:FormPropsType | {path:string})=>React.ReactNode;
}

The type used to describe object method props - FormPropsType

export type FormPropsType = {
  formName:string;
  onSubmit:ReturnType<typeof submitHandlersCreator>;
  changeFormStateHandler:ReturnType<changeFormStateHandlerType>;
}

The object itself

const authForms:AuthFormsType = {
  login:(props) =>{
    if(props === typeof FormPropsType ){
      return <Login 
      formName={props.fromName} 
      onSubmit={props.onSubmit} 
      changeFormStateHandler={props.changeFormStateHandler}
      />
    } 
    return <Login path={props.path} />
  },

I need to check what type props have and depending on what type to give this or that component?
What are the possible options for checking prop types?

Answer 1

There are no types in runtime, so you need to check according to what is, for example, write something like this typeguard:

const isFormPropsType = (v: FormPropsType | {path: string}): v is FormPropsType => typeof (v as FormPropsType).formName === 'string';

And accordingly use it to check:

const authForms:AuthFormsType = {
  login:(props) =>{
    if(isFormPropsType(props)){
      return <Login 
      formName={props.fromName} 
      onSubmit={props.onSubmit} 
      changeFormStateHandler={props.changeFormStateHandler}
      />
    } 
    return <Login path={props.path} />
  },

Although I suspect that it is much easier to do in this case:

const authForms:AuthFormsType = {
  login:(props) => {
    return <Login {...props} />
  },