How can I define a Typescript object return value for a function?

parseRange = (text: string) : { lower: number; upper: number; } => {
    // ...
    return {
        lower: lower,
        upper: upper
    };
};

or

parseRange = <(text: string) : { lower: number; upper: number; }> ((text) => {
    // ...
    return {
        lower: lower,
        upper: upper
    };
});

or

var parseRange : (text: string) => { lower: number; upper: number; } = (text) => {
    // ...
    return {
        lower: lower,
        upper: upper
    };
};

or

parseRange = function (text: string) : { lower: number; upper: number; } {
    // ...
    return {
        lower: lower,
        upper: upper
    };
};

or

function parseRange(text: string) : { lower: number; upper: number; } {
    // ...
    return {
        lower: lower,
        upper: upper
    };
};

or

interface RangeResult {
    lower: number;
    upper: number;
}
function parseRange(text: string) : RangeResult {
    // ...
    return {
        lower: lower,
        upper: upper
    };
};