diff --git a/pkg/argus_wasm_bg.wasm b/pkg/argus_wasm_bg.wasm
index e705a7e..0ace620 100644
Binary files a/pkg/argus_wasm_bg.wasm and b/pkg/argus_wasm_bg.wasm differ
diff --git a/src/lib.rs b/src/lib.rs
index c49b262..d47f356 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -101,7 +101,10 @@ pub struct StateBuddyTrace {
 
 #[wasm_bindgen]
 pub fn eval_boolean(s: &str, js_trace: JsValue) -> JsValue {
-    let trace: StateBuddyTrace = from_value(js_trace).expect("fuuuuck");
+    let trace: StateBuddyTrace = match from_value(js_trace) {
+        Ok(trace) => trace,
+        Err(e) => return JsValue::from_str("failed to parse JSON"),
+    };
     let mut traceMap = HashMap::<&str, Signal<bool>>::new();
     for entry in &trace.entries {
         let value = traceMap.entry(entry.inputEvent.as_str()).or_insert_with(|| Signal::<bool>::Sampled {
@@ -113,23 +116,31 @@ pub fn eval_boolean(s: &str, js_trace: JsValue) -> JsValue {
             time_points.push(Duration::from_millis(entry.simtime as u64));
         }
         else {
-            panic!("fuck!!!");
+            return JsValue::from_str("this should never happen");
         }
     }
 
     let parse_result = argus::parse_str(s);
-    let expr = parse_result.expect("fuuuckk!!");
+    let expr = match parse_result {
+        Ok(expr) => expr,
+        Err(e) => return JsValue::from_str("failed to parse expression"),
+    };
     let eval_result = match expr {
         Expr::Bool(bool_expr) => BooleanSemantics::eval::<interpolation::Constant>(&bool_expr, &TraceMap{events: traceMap}),
-        _ => panic!("fuuuck"),
+        _ => return JsValue::from_str("expected boolean expression (this should never happen)"),
     };
     let mut result = Vec::<StateBuddyEvalResultEntry>::new();
-    eval_result.expect("fuuuck").iter().for_each(|(timestamp, satisfied), | {
-        result.push(StateBuddyEvalResultEntry{
-            timestamp: timestamp.as_millis() as f64,
-            satisfied: *satisfied,
+    if let Ok(r) = eval_result {
+        r.iter().for_each(|(timestamp, satisfied), | {
+            result.push(StateBuddyEvalResultEntry{
+                timestamp: timestamp.as_millis() as f64,
+                satisfied: *satisfied,
+            });
         });
-    });
+    }
+    else {
+        return JsValue::from_str("failed to evaluate expression");
+    }
     to_value(&StateBuddyEvalResult { entries: result }).expect("fuuuck")
 }