nwjs/nw.js · error · Error

'type' is immutable at runtime

Error message

'type' is immutable at runtime

What it means

Thrown by the MenuItem 'type' setter whenever any value is assigned. The native menu item is created with a fixed type at construction; changing type (e.g. normal to separator) is not supported and would invalidate the native object, so the setter always throws.

Source

Thrown at src/resources/api_nw_menuitem.js:121

util.inherits(MenuItem, EventEmitter);

MenuItem.prototype.handleGetter = function(name) {
  return privates(this).option[name];
};

MenuItem.prototype.handleSetter = function(name, setter, type, value) {
  value = type(value);
  privates(this).option[name] = value;
  nw.Obj.callObjectMethod(this.id, 'MenuItem', setter, [ value ]);
};

MenuItem.prototype.__defineGetter__('type', function() {
  return this.handleGetter('type');
});

MenuItem.prototype.__defineSetter__('type', function() {
  throw new Error("'type' is immutable at runtime");
});

MenuItem.prototype.__defineGetter__('label', function() {
  return this.handleGetter('label');
});

MenuItem.prototype.__defineSetter__('label', function(val) {
  this.handleSetter('label', 'SetLabel', String, val);
});

MenuItem.prototype.__defineGetter__('icon', function() {
  return this.handleGetter('shadowIcon');
});

MenuItem.prototype.__defineSetter__('icon', function(val) {
  privates(this).option.shadowIcon = String(val);
  var real_path = val == '' ? '' : nwNative.getAbsolutePath(val); //FIXME
  this.handleSetter('icon', 'SetIcon', String, real_path);

View on GitHub (pinned to e15da848e9)

Solutions

1. Create a new MenuItem of the desired type and replace it in the menu (append the new one, remove the old).
2. To hide an item, use item.visible = false rather than changing its type.

Example fix

// before
item.type = 'separator';
// after
const sep = new nw.MenuItem({ type: 'separator' });
menu.insert(sep, menu.items.indexOf(item));
menu.remove(item);

// never assign to item.type; rebuild the item instead

function isMutableMenuItemProp(p) { return ['label', 'icon', 'enabled', 'checked', 'tooltip', 'modifiers'].indexOf(p) !== -1; }

try { item.type = t; } catch (e) { if (/immutable/.test(e.message)) console.warn('type is immutable; rebuild the item'); else throw e; }

When it happens

Trigger: Running `item.type = 'separator'`, `item.type = 'checkbox'`, or any assignment to .type after construction.

Common situations: Trying to toggle an item between a normal entry and a divider dynamically; porting UI code that mutated type.

Related errors

• 'type' is immutable at runtime
• Menu.items is immutable
• 'checked' property is only available for checkbox
• Menu.items is immutable
• Menu.append() requires a valid MenuItem

AI-assisted analysis of nwjs/nw.js@e15da848e9 (2026-08-13). Data as JSON: /api/errors/af2a057213dfa629. Report an issue: GitHub.