disconnecting mutation observer on disconnect

src/compiler/compile/render_dom/index.ts

@@ -446,8 +446,8 @@ export default function dom(
 						this._root =this.attachShadow({ mode: '${options.shadowDom}' });
 					` || b`
 						this._copycontent();
-						const observer = new MutationObserver(() => this._slotcontent());
+						this.slotObserver = new MutationObserver(() => this._slotcontent());
-						observer.observe(this, {childList: true, subtree: true});
+						this.slotObserver.observe(this, {childList: true, subtree: true});
 					`}
 					${css.code && !lightDom && b`this._root.innerHTML = \`<style>${css.code.replace(/\\/g, '\\\\')}${options.dev ? `\n/*# sourceMappingURL=${css.map.toUrl()} */` : ''}</style>\`;`}
 					${should_add_css && lightDom && b`if (!@_document.getElementById("${component.stylesheet.id}-style")) ${add_css}();`}
@@ -544,6 +544,17 @@ export default function dom(
 					}
 				}` as FunctionExpression
 			});
+
+			declaration.body.body.push({
+				type: 'MethodDefinition',
+				kind: 'method',
+				static: false,
+				computed: false,
+				key: { type: 'Identifier', name: 'disconnectedCallback' },
+				value: x`function() {
+					this.slotObserver.disconnect();
+				}` as FunctionExpression
+			});
 		}
 
 		declaration.body.body.push(...accessors);