No-update mode for "want to read"

bookwyrm/static/js/bookwyrm.js

@@ -177,6 +177,12 @@ let BookWyrm = new class {
             this.toggleCheckbox(checkbox, pressed);
         }
 
+        // Toggle form disabled, if appropriate
+        let disable = trigger.dataset.disables;
+        if (disable) {
+            this.toggleDisabled(disable, !pressed);
+        }
+
         // Set focus, if appropriate.
         let focus = trigger.dataset.focusTarget;
 
@@ -227,6 +233,17 @@ let BookWyrm = new class {
         document.getElementById(checkbox).checked = !!pressed;
     }
 
+    /**
+     * Enable or disable a form element or fieldset
+     *
+     * @param  {string}  form_element - id of the element
+     * @param  {boolean} pressed  - Is the trigger pressed?
+     * @return {undefined}
+     */
+    toggleDisabled(form_element, pressed) {
+        document.getElementById(form_element).disabled = !!pressed;
+    }
+
     /**
      * Give the focus to an element.
      * Only move the focus based on user interactions.