React function component prop default with TypeScript

Question

I'm having trouble with a React function component and defaulting a required prop.

Here's the component:

type Props = { message: string };
function Greeting({ message = "How are you?" }: Props) {
  return <p>{message}</p>;
}

I should be able to consume it without passing the message prop:

<Greeting />

However, TypeScript raises a type error Property 'message' is missing in type '{}' but required in type 'Props':

Here's the issue in a CodeSandbox: https://codesandbox.io/s/still-microservice-lp7b5?fontsize=14&hidenavigation=1&theme=dark

I wasn't sure whether I am doing something wrong or whether this is a glitch in TypeScript? Any help would be appreciated.

This needs to be used as an example question somewhere. Very well asked. — Thoth
– Thoth, Commented Feb 11, 2020 at 19:18
Property 'message' is missing in type '{}' but required in type 'Props'.ts It says you have required props type. Which is why typescript screams for this :) Just change type props like this message?:string. — sajan
– sajan, Commented Feb 11, 2020 at 19:18

Samuel Hulla · Accepted Answer · 2020-02-11 19:15:58Z

3

Your Props type definition has a required argument of message, however you're treating it as an optional argument. This is also referenced in the error message you're getting

Property 'message' is missing in type '{}' but required in type 'Props'
Understand the error message as - your type Props has a required property of message however, your provided type {}, which is missing it (read {} as no provided properties)

Change the definition to the following way:

type Props = {
   message?: string; //< note the '?' at the end of property
};

Now if the component is returned without a specific message prop, it will default to "How are you?"

edited Feb 11, 2020 at 19:15

answered Feb 11, 2020 at 19:02

Samuel Hulla

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