first commit

js/form_helper.js

@@ -0,0 +1,26 @@
+const inputs = document.querySelectorAll("input")
+
+inputs.forEach(input => {
+    input.addEventListener(
+        "invalid",
+        () => {
+            input.classList.add("error")
+            input.nextElementSibling.style.display = "inline"
+        },
+        false
+    )
+
+    input.addEventListener(
+        "input",
+        event => checkValidityOnInput(event),
+        false
+    )
+})
+
+function checkValidityOnInput(e){
+    e.target.checkValidity()
+    if(e.target.validity.valid) {
+        e.target.classList.remove("error")
+        e.target.nextElementSibling.style.display = "none"
+    }
+}