introduced a StandardWidget base class

src/public/javascripts/widgets/standard_widget.js

@@ -0,0 +1,77 @@
+const WIDGET_TPL = `
+<div class="card widget">
+    <div class="card-header">        
+        <button class="btn btn-sm widget-title" data-toggle="collapse" data-target="#[to be set]">
+            Collapsible Group Item
+        </button>
+        
+        <div class="widget-header-actions"></div>
+    </div>
+
+    <div id="[to be set]" class="collapse body-wrapper">
+        <div class="card-body"></div>
+    </div>
+</div>
+`;
+
+class StandardWidget {
+    /**
+     * @param {TabContext} ctx
+     * @param {object} state
+     * @param {string} widgetId
+     */
+    constructor(ctx, state, widgetId) {
+        this.ctx = ctx;
+        this.widgetId = widgetId;
+
+        this.$widget = $(WIDGET_TPL);
+        this.$widget.find('[data-target]').attr('data-target', "#widget-" + widgetId);
+
+        this.$bodyWrapper = this.$widget.find('.body-wrapper');
+        this.$bodyWrapper.attr('id', "widget-" + widgetId);
+
+        if (state && state.visible) {
+            this.$bodyWrapper.addClass("show");
+        }
+
+        this.$body = this.$bodyWrapper.find('.card-body');
+
+        this.$widget.on('shown.bs.collapse', () => this.renderBody());
+        this.$widget.on('shown.bs.collapse', () => this.ctx.stateChanged());
+        this.$widget.on('hidden.bs.collapse', () => this.ctx.stateChanged());
+        this.$title = this.$widget.find('.widget-title');
+        this.$headerActions = this.$widget.find('.widget-header-actions');
+    }
+
+    async renderBody() {
+        if (!this.isVisible() || this.rendered) {
+            return;
+        }
+
+        this.rendered = true;
+
+        await this.doRenderBody();
+    }
+
+    /** for overriding */
+    async doRenderBody() {}
+
+    isVisible() {
+        return this.$bodyWrapper.is(":visible");
+    }
+
+    getWidgetState() {
+        return {
+            id: this.widgetId,
+            visible: this.isVisible()
+        };
+    }
+
+    getWidgetElement() {
+        return this.$widget;
+    }
+
+    syncDataReceived(syncData) {}
+}
+
+export default StandardWidget;