gistfile1.js

var totalPages = 50, buttons = 3;
var currentPage = lowerLimit = upperLimit = Math.min(50, totalPages);

for (var b = 1; b < buttons && b < totalPages;) {
    if (lowerLimit > 1 ) { lowerLimit--; b++; }
    if (b < buttons && upperLimit < totalPages) { upperLimit++; b++; }
}