It is incorrectly defined as no arguments in both lib.d.ts as well as the most recent DefinitelyTyped date.format.d.ts

See spec

I believe it should be this:

toLocaleDateString(locales?: string[] | string, options?: Intl.DateTimeFormatOptions): string;

JavaScript example:

var date = new Date(Date.UTC(2015, 8, 12, 9, 41, 0));
console.log(date.toLocaleDateString(['en-US'], { month: "2-digit" }));
// will write "08" to the console

NOTE: I believe toLocaleTimeString has the same problem.

I am willing to submit a pull request -- I'm just not that familiar with writing jake tests.