I am new to typescript and I was wondering if there is a way to make a type required based on the value of another type:
type TextInput = {
isValid?: boolean;
validMessage?: string;
}
Is it possible to make validMessage required if isValid becomes true?
You need to use discriminated unions:
type Valid = {
isValid: true;
validMessage: string
}
type Invalid = {
isValid: false;
}
type TextInput = Valid | Invalid
const foo = (props: TextInput) => {
if (props.isValid) {
props.validMessage // ok
} else {
props.isValid // false
props.validMessage // error
}
}
See also related docs