discriminated-union.tsx

type SharedProps = {
    multiple: boolean;
    name: string;
}

type Multiple = SharedProps & {
    multiple: true;
    callback: (items: string[]) => void;
}

type Single = SharedProps & {
    multiple: false;
    callback: (item: string) => void;
}

function UploadComponent({multiple, callback}: Single | Multiple) {
    function handleClick() {
        if (multiple){
            callback(["1", "2", "3"])
        } else {
            callback("1")
        }
    }

    return (
        <button onClick={handleClick}>Run callback</button>
    )
}