{"record":{"id":"bfa3234ac4640e26","repo":"yewstack/yew","slug":"mouse-event-doesn-t-have-a-target-bfa323","errorCode":null,"errorMessage":"mouse event doesn't have a target","messagePattern":"mouse event doesn't have a target","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"website/versioned_docs/version-0.23/concepts/basic-web-technologies/web-sys.mdx","lineNumber":172,"sourceCode":"version = \"0.3\"\n# We need to enable all the web-sys features we want to use!\nfeatures = [\n    \"console\",\n    \"Document\",\n    \"HtmlElement\",\n    \"MouseEvent\",\n    \"DomRect\",\n]\n```\n\n```rust ,no_run\nuse wasm_bindgen::{prelude::Closure, JsCast};\nuse web_sys::{console, Document, HtmlElement, MouseEvent};\n\nlet mousemove = Closure::<dyn Fn(MouseEvent)>::wrap(Box::new(|e: MouseEvent| {\n    let rect = e\n        .target()\n        .expect(\"mouse event doesn't have a target\")\n        .dyn_into::<HtmlElement>()\n        .expect(\"event target should be of type HtmlElement\")\n        .get_bounding_client_rect();\n    let x = (e.client_x() as f64) - rect.left();\n    let y = (e.client_y() as f64) - rect.top();\n    console::log_1(&format!(\"Left? : {} ; Top? : {}\", x, y).into());\n}));\n\nDocument::new()\n    .expect(\"global document not set\")\n    .get_element_by_id(\"mousemoveme\")\n    .expect(\"element with id `mousemoveme` not present\")\n    .unchecked_into::<HtmlElement>()\n    .set_onmousemove(mousemove.as_ref().dyn_ref());\n\n// we now need to save the `mousemove` Closure so that when\n// this event fires the closure is still in memory.\n```","sourceCodeStart":154,"sourceCodeEnd":190,"githubUrl":"https://github.com/yewstack/yew/blob/0e4a05472fac4e5fce1befe60fa4a1e43a36b6a3/website/versioned_docs/version-0.23/concepts/basic-web-technologies/web-sys.mdx#L154-L190","documentation":"This panic is `.expect(\"mouse event doesn't have a target\")` on `e.target()` in the mousemove closure of Yew 0.23's web-sys guide (note the closure now annotates `|e: MouseEvent|`). `MouseEvent::target()` returns `Option<EventTarget>`; None occurs only for programmatic events that were never dispatched on a node — real mousemove events delivered to a `set_onmousemove` handler always carry a target.","triggerScenarios":"Invoking the closure directly in a test with `MouseEvent::new().unwrap()` (no dispatch, target None); routing synthetic mouse events through a custom dispatcher that never assigns targets.","commonSituations":"Copy-pasting the 0.23 web-sys.mdx coordinate snippet into examples or test harnesses that fabricate events instead of simulating real pointer input.","solutions":["Skip targetless events: `let Some(target) = e.target() else { return; };`","Prefer `e.current_target()` for coordinates relative to the bound element — always present and always that element","In tests, dispatch mousemove from a real element so the target is set"],"exampleFix":"// before\nlet rect = e\n    .target()\n    .expect(\"mouse event doesn't have a target\")\n    .dyn_into::<HtmlElement>()\n    .expect(\"event target should be of type HtmlElement\")\n    .get_bounding_client_rect();\n\n// after\nlet rect = e\n    .current_target()\n    .dyn_into::<HtmlElement>()\n    .ok()?\n    .get_bounding_client_rect();","handlingStrategy":"validation","validationCode":"let mousemove = Closure::<dyn Fn(MouseEvent)>::wrap(Box::new(|e: MouseEvent| {\n    let Some(target) = e.target() else {\n        return;\n    };\n    let _ = target;\n}));","typeGuard":"use wasm_bindgen::JsCast;\nuse web_sys::{EventTarget, HtmlElement, MouseEvent};\n\nfn target_element(e: &MouseEvent) -> Option<HtmlElement> {\n    e.target()?.dyn_into::<HtmlElement>().ok()\n}","tryCatchPattern":null,"preventionTips":["Use current_target() for listener-relative coordinate math","let-else skip targetless events instead of expect","Dispatch synthetic mousemove from a real element in tests"],"tags":["web-sys","events","mouse","option-expect","panic"],"backgroundTag":"event-target-missing","analyzedSha":"0e4a05472fac4e5fce1befe60fa4a1e43a36b6a3","analyzedAt":"2026-08-22T21:16:31.212Z","schemaVersion":2},"datasetVersion":"2026-08-23T01:17:44.959Z"}