Property name on object from variable

You are looking for computed properties, this is an ES6 feature and not specific to TypeScript.

export function objectFactory(prop: string) {
    return {
        [prop]: {
            valid: false
        }
    };
}

You can do it like this:

export function objectFactory(prop: string) {
    let data: any = {};
    data[prop] = {};
    data[prop].valid = false;
    return data;
}