pageNumber - current page number counted from 1 to up (1, 2, 3, ...),
pagesCount - total number of pages,
radiusSize - maximal number of buttons visible on both sides of active page button.

Custom Vanilla JS pager component example.

Practical example

As radius, we understand number of items displayed on left and right site of current page button.

Note: using component, replace /path/to/page/... with correct url.

// ONLINE-RUNNER:browser;

<!doctype html>
<html>
<head>
  <style>

    div.pager {
    	padding: 20px 0;
    }
    
    a.link { 
    	padding: 5px 10px;
      	text-decoration: none;
      	color: #007bff;
    }

    a.button { 
      	padding: 5px 10px;
      	border: 1px solid;
      	border-radius: 3px;
      	text-decoration: none;
    }
    
    a.button + a.button {
    	margin-left: 5px;
    }
    
    a.button.default {
      	border-color: #66b0ff;
    	background-color: white;
      	color: #007bff;
    }
    
    a.button.default:hover {
    	border-color: #007bff;
        background-color: #e0efff;
    }
    
    a.button.selected {
    	border-color: #007bff;
        background-color: #007bff;
      	color: white;
    }

  </style>
</head>
<body>
  <div id="pager-container"></div>
  <script>
    
    function calculateRange(pageNumber, pagesCount, radiusSize) {
        var start = pageNumber - radiusSize;
        if (start < 1) {
            return {
                start: 1,
                stop: Math.min(2 * radiusSize + 1, pagesCount),
            };
        }
        var stop = pageNumber + radiusSize;
        if (stop > pagesCount) {
            return {
                start: Math.max(1, pagesCount - 2 * radiusSize),
                stop: pagesCount,
            };
        }
        return { start, stop };
    }
    
    function renderPager(pageNumber, pagesCount, radiusSize) {
      	var pager = '';
    	var range = calculateRange(pageNumber, pagesCount, radiusSize);
      	pager += '<div class="pager">';
      	pager +=	'<a class="link" href="/path/to/page/1">First</a>';
      	for (var i = range.start; i <= range.stop; ++i) {
          	var buttonClass = 'button ' + (i === pageNumber ? 'selected' : 'default');
          	var pagePath = '/path/to/page/' + i;
        	pager += '<a class="' + buttonClass + '" href="' + pagePath + '">' +
                        i +
                     '</a>'
        }
      	pager += '<a class="link" href="/path/to/page/' + pagesCount + '">Last</a>';
      	pager += '</div>';
      	return pager;
    }
    
    // Usage example:
    
    var container = document.querySelector('#pager-container');

    container.innerHTML += renderPager(1, 6, 2);
	container.innerHTML += renderPager(3, 6, 2);
	container.innerHTML += renderPager(4, 6, 2);
	container.innerHTML += renderPager(6, 6, 2);

  </script>
</body>
</html>