Add initial versions

form-element.js

@@ -0,0 +1,51 @@
+/**
+@license
+Copyright (c) 2022 trading_peter
+This program is available under Apache License Version 2.0
+*/
+
+export const FormElement = function(superClass) {
+  return class extends superClass {
+    static get properties() {
+      return {
+        // The name of this element.
+        name: { type: String },
+
+        // The value for this element.
+        value: { type: String },
+
+        // Set to true to mark the input as required. Element needs to provide a "validate()" function tha returns a boolean.
+        required: { type: Boolean },
+
+        // The form that the element is registered to. Set by the form that got the registration.
+        parentForm: { type: Object }
+      };
+    }
+
+    connectedCallback() {
+      super.connectedCallback();
+
+      // Prevent that child elements register.
+      this.addEventListener('form-element-register', this._onChildRegister.bind(this));
+    }
+
+    firstUpdated() {
+      super.firstUpdated();
+      this.dispatchEvent(new CustomEvent('form-element-register', { bubbles: true, composed: true }));
+    }
+
+    disconnectedCallback() {
+      super.disconnectedCallback();
+      if (this._parentForm) {
+        this._parentForm.dispatchEvent(new CustomEvent('form-element-unregister', { detail: { target: this }, bubbles: true, composed: true }));
+      }
+    }
+
+    // Prevent that child elements register themselves to the form element.
+    _onChildRegister(e) {
+      if (e.composedPath()[0].tagName !== this.tagName) {
+        e.stopPropagation();
+      }
+    }
+  };
+}