diff --git a/doc/scripts/header.js b/doc/scripts/header.js
index 13a707e..d445c9a 100644
--- a/doc/scripts/header.js
+++ b/doc/scripts/header.js
@@ -1,34 +1,30 @@
-var domReady = function(callback) {
-	var state = document.readyState ;
-    if ( state === 'interactive' || state === 'complete' ) {
-		callback() ;
-	}
-	else {
+const domReady = function (callback) {
+	const state = document.readyState;
+	if (state === 'interactive' || state === 'complete') {
+		callback();
+	} else {
 		document.addEventListener('DOMContentLoaded', callback);
 	}
-} ;
-
+};
 
-domReady(function(){
-
-	var projectname = document.createElement('a');
+domReady(function () {
+	const projectname = document.createElement('a');
 	projectname.classList.add('project-name');
 	projectname.text = 'aureooms/js-knapsack';
-	projectname.href = './index.html' ;
+	projectname.href = './index.html';
 
-	var header = document.getElementsByTagName('header')[0] ;
-	header.insertBefore(projectname,header.firstChild);
+	const header = document.querySelectorAll('header')[0];
+	header.insertBefore(projectname, header.firstChild);
 
-	var testlink = document.querySelector('header > a[data-ice="testLink"]') ;
-	testlink.href = 'https://coveralls.io/github/aureooms/js-knapsack' ;
-	testlink.target = '_BLANK' ;
+	const testlink = document.querySelector('header > a[data-ice="testLink"]');
+	testlink.href = 'https://coveralls.io/github/aureooms/js-knapsack';
+	testlink.target = '_BLANK';
 
-	var searchBox = document.querySelector('.search-box');
-	var input = document.querySelector('.search-input');
+	const searchBox = document.querySelector('.search-box');
+	const input = document.querySelector('.search-input');
 
-	// active search box when focus on searchBox.
-	input.addEventListener('focus', function(){
+	// Active search box when focus on searchBox.
+	input.addEventListener('focus', function () {
 		searchBox.classList.add('active');
 	});
-
 });