yewstack/yew · error

couldn't clone node to be cached

Error message

couldn't clone node to be cached

What it means

On the first render of a tag name (cache miss), Yew creates the element and immediately clones it once more to store as the template in CACHED_ELEMENTS; this expect fires when that clone fails. Like the sibling 'couldn't clone cached element' panic at line 295, cloning a freshly created element is an internal invariant - a failure points at an exotic element constructor (custom elements throwing during the extra clone) or a non-standard DOM host, not at normal application code.

Source

Thrown at packages/yew/src/dom_bundle/btag/mod.rs:306

                        static CACHED_ELEMENTS: RefCell<HashMap<String, Element>> = RefCell::new(HashMap::with_capacity(32));
                    }

                    CACHED_ELEMENTS.with(|cache| {
                        let mut cache = cache.borrow_mut();
                        let cached = cache.get(tag).map(|el| {
                            el.clone_node()
                                .expect("couldn't clone cached element")
                                .unchecked_into::<Element>()
                        });
                        cached.unwrap_or_else(|| {
                            let to_be_cached = document()
                                .create_element(tag)
                                .expect("can't create element for vtag");
                            cache.insert(
                                tag.to_string(),
                                to_be_cached
                                    .clone_node()
                                    .expect("couldn't clone node to be cached")
                                    .unchecked_into(),
                            );
                            to_be_cached
                        })
                    })
                }
            }
        }
    }
}

impl BTag {
    /// Get the key of the underlying tag
    pub fn key(&self) -> Option<&Key> {
        self.key.as_ref()
    }

    #[cfg(all(target_arch = "wasm32", not(target_os = "wasi")))]

View on GitHub (pinned to 0e4a05472f)

Solutions

  1. Identify which tag caused the cache miss from the html!/VTag construction nearest the panic stack
  2. Reproduce in the browser console: const el = document.createElement('<tag>'); el.cloneNode(); - if that throws, the element definition is the problem
  3. Make custom-element constructors safe when the element is disconnected
  4. If a plain tag reproduces it, report a Yew issue with a minimal repro and environment details
Defensive patterns

Strategy: validation

Validate before calling

// Before relying on a custom tag in Yew, smoke-test it once in the console:
// const el = document.createElement('x-widget'); el.cloneNode();
// Both calls must succeed for Yew's create-and-cache flow to hold.

Prevention

When it happens

Trigger: The very first render of a tag in the session (cache miss) where the constructor of the created element throws during the additional cloneNode() call - typically a registered custom element - or an embedded webview/test DOM where cloneNode can fail.

Common situations: Web components whose constructors assume connection or layout; unusual webviews with partial DOM implementations; Yew internal regressions. Standard tags (div, span, a) are not expected to hit this in any mainstream browser.

Related errors

AI-assisted analysis of yewstack/yew@0e4a05472f (2026-08-22). Data as JSON: /api/errors/29be2073ec91eea4. Report an issue: GitHub.