Add sharing functionality

src/index.pug

@@ -12,14 +12,14 @@ html(lang="en")
             h1 toot
             p Share links on any Mastodon instance
         main
-            form
+            form#form
                 section
                     label(for="instance") Mastodon instance URL
-                    input#instance(type="url", name="instance", placeholder="https://")
+                    input#instance(type="url", name="instance", placeholder="https://", required)
 
                 section.remember
                     input#remember(type="checkbox", name="remember")
-                    label(for="remember") Remember as my default instance
+                    label(for="remember") Autofill this instance URL next time
 
                 section.submit
                     input(type="submit", value="Share post")

src/script/index.js

@@ -0,0 +1,39 @@
+var remembered = window.localStorage.getItem('mastodon_instance');
+if (remembered != null) {
+    document.getElementById('instance').value = remembered;
+}
+
+var parsedQuery = {};
+
+var paramPairs = window.location.search.substr(1).split('&');
+var paramPairsLength = paramPairs.length;
+
+for (var i = 0; i < paramPairsLength; i++) {
+    var paramPair = paramPairs[i].split('=');
+    parsedQuery[paramPair[0]] = paramPair[1];
+}
+delete i
+delete paramPair
+
+document
+  .getElementById('form')
+  .addEventListener('submit', function (e) {
+    e.preventDefault();
+    var instance = e.target.elements['instance'].value;
+    var remember = e.target.elements['remember'].checked;
+
+
+    if (!(instance.startsWith("https://") || instance.startsWith("http://"))) {
+        instance = "https://" + instance;
+    }
+    if (!instance.endsWith("/")){
+        instance = instance + "/";
+    }
+
+    if (remember) {
+        window.localStorage.setItem('mastodon_instance', instance);
+    }
+
+    var shareUrl = instance + "share?text=" + parsedQuery.text;
+    window.open(shareUrl, '_blank', 'noopener,noreferrer')
+})