Updated search suggestion behavior (closes #115)

Arrow key navigation through search suggestions now populates the input
field with text content from the active selection. Navigating "down"
past the end of the suggestions list returns the active cursor to position 0,
while navigating "up" before the list of suggestions restores the
original search query and removes the active highlight from element 0.

app/static/js/autocomplete.js

@@ -2,7 +2,7 @@ const handleUserInput = searchBar => {
     let xhrRequest = new XMLHttpRequest();
     xhrRequest.open("POST", "/autocomplete");
     xhrRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
-    xhrRequest.onload = function() {
+    xhrRequest.onload = function () {
         if (xhrRequest.readyState === 4 && xhrRequest.status !== 200) {
             // Do nothing if failed to fetch autocomplete results
             return;
@@ -18,6 +18,7 @@ const handleUserInput = searchBar => {
 
 const autocomplete = (searchInput, autocompleteResults) => {
     let currentFocus;
+    let originalSearch;
 
     searchInput.addEventListener("input", function () {
         let autocompleteList, autocompleteItem, i, val = this.value;
@@ -53,9 +54,11 @@ const autocomplete = (searchInput, autocompleteResults) => {
         let suggestion = document.getElementById(this.id + "-autocomplete-list");
         if (suggestion) suggestion = suggestion.getElementsByTagName("div");
         if (e.keyCode === 40) { // down
+            e.preventDefault();
             currentFocus++;
             addActive(suggestion);
         } else if (e.keyCode === 38) { //up
+            e.preventDefault();
             currentFocus--;
             addActive(suggestion);
         } else if (e.keyCode === 13) { // enter
@@ -63,17 +66,36 @@ const autocomplete = (searchInput, autocompleteResults) => {
             if (currentFocus > -1) {
                 if (suggestion) suggestion[currentFocus].click();
             }
+        } else {
+            originalSearch = document.getElementById("search-bar").value;
         }
     });
 
     const addActive = suggestion => {
-        if (!suggestion || !suggestion[currentFocus]) return false;
-        removeActive(suggestion);
+        let searchBar = document.getElementById("search-bar");
 
-        if (currentFocus >= suggestion.length) currentFocus = 0;
-        if (currentFocus < 0) currentFocus = (suggestion.length - 1);
+        // Handle navigation outside of suggestion list
+        if (!suggestion || !suggestion[currentFocus]) {
+            if (currentFocus >= suggestion.length) {
+                // Move selection back to the beginning
+                currentFocus = 0;
+            } else if (currentFocus < 0) {
+                // Retrieve original search and remove active suggestion selection
+                currentFocus = -1;
+                searchBar.value = originalSearch;
+                removeActive(suggestion);
+                return;
+            } else {
+                return;
+            }
+        }
 
+        removeActive(suggestion);
         suggestion[currentFocus].classList.add("autocomplete-active");
+
+        // Autofill search bar with suggestion content
+        searchBar.value = suggestion[currentFocus].textContent;
+        searchBar.focus();
     };
 
     const removeActive = suggestion => {