in compare method why we taking a and b for sorting in javascript

1for compare and sort method:-
2  
3function compare(a,b) {
4    return a - b;
5}
6------------------
7
8var numbers = [1,5,3.14];
9compare(1,5);     // Returns -4, a is less than b
10compare(1,3.14);  // Return -2.14, a is less than b
11compare(5,3.14);  // returns 1.86, a is greater than b