MD5, understand/modify script in Javascript?

Question

JavaScript

Greetings! I am a beginner in such matters, but I want to check something, please help. In general, there is a roulette script that hashes the verification string in MD5.

Example:
123.45.67890
123 - roulette number
45 - hidden number
67890 - random
MD5 value - fa52d9f98c6ea8d4ea6750a234835ada

calc = function () {
            var form = $("#round-calculator");
            var number = form.find("input#round_win_num").val().trim();
            var id = form.find("input#round_id").val().trim();
            $('#md5').val(md5(id+'.'+$(this).val()));
            if(!number || !id){
                $('#md5').val('Хэш раунда');
            }else{
                $('#md5').val(md5(id+'.'+number));
            }
        };

I don't understand what +$( this ).val() means , and how +number is generated .
I'm also interested in how you can build a script so that it would sort of brute +number , with an already given id and a selected number. In short, what would I ask, let's say half of the string " 123.45 . "