Required/optional props depending on another prop/flag

conditional_prop_types.ts

interface CommonProps {
    a: number
    b: string
}

interface EnabledProps {
    onChangeFn: (newVal: string) => void
}

type ConditionalProps =
    | ({ disabled: true } & Partial<EnabledProps>)
    | ({ disabled?: false} & Required<EnabledProps>)

type Props = CommonProps & ConditionalProps

const props1: Props = {
    a: 1,
    b: 'foo',
    onChangeFn: () => {}
}

// Property 'onChangeFn' is missing in type '{ a: number; b: string; }' but required in type 'Required<EnabledProps>'
const props2: Props = {
    a: 1,
    b: 'foo',
}

const props3: Props = {
    a: 1,
    b: 'foo',
    disabled: true,
}