If you format it differently, you can see that this might look like TS, but it's just JavaScript. Coincidentally, the angle brackets and the comma match perfectly with the syntax for the two arguments of console.log, where each is a comparison, less than and greater than. What is being compared is:

new Map < String // true
Number > [] // true

Written out in a way that makes this more obvious:

console.log(new Map < String, Number > ([]))

If you meant to write this in a TS file where it might get interpreted (as you may have intended) as a type generic, then you are probably looking for different types: string and number, rather than the String and Number constructors that you used in the example.