diff --git a/pkg/argus_wasm.js b/pkg/argus_wasm.js
index 1356d94..d89319b 100644
--- a/pkg/argus_wasm.js
+++ b/pkg/argus_wasm.js
@@ -30,6 +30,69 @@ function getStringFromWasm0(ptr, len) {
     return decodeText(ptr, len);
 }
 
+let WASM_VECTOR_LEN = 0;
+
+const cachedTextEncoder = new TextEncoder();
+
+if (!('encodeInto' in cachedTextEncoder)) {
+    cachedTextEncoder.encodeInto = function (arg, view) {
+        const buf = cachedTextEncoder.encode(arg);
+        view.set(buf);
+        return {
+            read: arg.length,
+            written: buf.length
+        };
+    }
+}
+
+function passStringToWasm0(arg, malloc, realloc) {
+
+    if (realloc === undefined) {
+        const buf = cachedTextEncoder.encode(arg);
+        const ptr = malloc(buf.length, 1) >>> 0;
+        getUint8ArrayMemory0().subarray(ptr, ptr + buf.length).set(buf);
+        WASM_VECTOR_LEN = buf.length;
+        return ptr;
+    }
+
+    let len = arg.length;
+    let ptr = malloc(len, 1) >>> 0;
+
+    const mem = getUint8ArrayMemory0();
+
+    let offset = 0;
+
+    for (; offset < len; offset++) {
+        const code = arg.charCodeAt(offset);
+        if (code > 0x7F) break;
+        mem[ptr + offset] = code;
+    }
+
+    if (offset !== len) {
+        if (offset !== 0) {
+            arg = arg.slice(offset);
+        }
+        ptr = realloc(ptr, len, len = offset + arg.length * 3, 1) >>> 0;
+        const view = getUint8ArrayMemory0().subarray(ptr + offset, ptr + len);
+        const ret = cachedTextEncoder.encodeInto(arg, view);
+
+        offset += ret.written;
+        ptr = realloc(ptr, len, offset, 1) >>> 0;
+    }
+
+    WASM_VECTOR_LEN = offset;
+    return ptr;
+}
+
+let cachedDataViewMemory0 = null;
+
+function getDataViewMemory0() {
+    if (cachedDataViewMemory0 === null || cachedDataViewMemory0.buffer.detached === true || (cachedDataViewMemory0.buffer.detached === undefined && cachedDataViewMemory0.buffer !== wasm.memory.buffer)) {
+        cachedDataViewMemory0 = new DataView(wasm.memory.buffer);
+    }
+    return cachedDataViewMemory0;
+}
+
 function isLikeNone(x) {
     return x === undefined || x === null;
 }
@@ -99,69 +162,6 @@ function debugString(val) {
     return className;
 }
 
-let WASM_VECTOR_LEN = 0;
-
-const cachedTextEncoder = new TextEncoder();
-
-if (!('encodeInto' in cachedTextEncoder)) {
-    cachedTextEncoder.encodeInto = function (arg, view) {
-        const buf = cachedTextEncoder.encode(arg);
-        view.set(buf);
-        return {
-            read: arg.length,
-            written: buf.length
-        };
-    }
-}
-
-function passStringToWasm0(arg, malloc, realloc) {
-
-    if (realloc === undefined) {
-        const buf = cachedTextEncoder.encode(arg);
-        const ptr = malloc(buf.length, 1) >>> 0;
-        getUint8ArrayMemory0().subarray(ptr, ptr + buf.length).set(buf);
-        WASM_VECTOR_LEN = buf.length;
-        return ptr;
-    }
-
-    let len = arg.length;
-    let ptr = malloc(len, 1) >>> 0;
-
-    const mem = getUint8ArrayMemory0();
-
-    let offset = 0;
-
-    for (; offset < len; offset++) {
-        const code = arg.charCodeAt(offset);
-        if (code > 0x7F) break;
-        mem[ptr + offset] = code;
-    }
-
-    if (offset !== len) {
-        if (offset !== 0) {
-            arg = arg.slice(offset);
-        }
-        ptr = realloc(ptr, len, len = offset + arg.length * 3, 1) >>> 0;
-        const view = getUint8ArrayMemory0().subarray(ptr + offset, ptr + len);
-        const ret = cachedTextEncoder.encodeInto(arg, view);
-
-        offset += ret.written;
-        ptr = realloc(ptr, len, offset, 1) >>> 0;
-    }
-
-    WASM_VECTOR_LEN = offset;
-    return ptr;
-}
-
-let cachedDataViewMemory0 = null;
-
-function getDataViewMemory0() {
-    if (cachedDataViewMemory0 === null || cachedDataViewMemory0.buffer.detached === true || (cachedDataViewMemory0.buffer.detached === undefined && cachedDataViewMemory0.buffer !== wasm.memory.buffer)) {
-        cachedDataViewMemory0 = new DataView(wasm.memory.buffer);
-    }
-    return cachedDataViewMemory0;
-}
-
 function addToExternrefTable0(obj) {
     const idx = wasm.__externref_table_alloc();
     wasm.__wbindgen_externrefs.set(idx, obj);
@@ -235,6 +235,13 @@ function __wbg_get_imports() {
         const ret = Error(getStringFromWasm0(arg0, arg1));
         return ret;
     };
+    imports.wbg.__wbg_String_8f0eb39a4a4c2f66 = function(arg0, arg1) {
+        const ret = String(arg1);
+        const ptr1 = passStringToWasm0(ret, wasm.__wbindgen_malloc, wasm.__wbindgen_realloc);
+        const len1 = WASM_VECTOR_LEN;
+        getDataViewMemory0().setInt32(arg0 + 4 * 1, len1, true);
+        getDataViewMemory0().setInt32(arg0 + 4 * 0, ptr1, true);
+    };
     imports.wbg.__wbg___wbindgen_boolean_get_6d5a1ee65bab5f68 = function(arg0) {
         const v = arg0;
         const ret = typeof(v) === 'boolean' ? v : undefined;
diff --git a/pkg/argus_wasm_bg.wasm b/pkg/argus_wasm_bg.wasm
index 105a6ad..e350e51 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 dd50dd6..2218c3e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -52,7 +52,7 @@ pub fn eval_boolean(s: &str, js_trace: JsValue) -> JsValue {
     // convert input (a sequence of state-objects) to a Trace that argus accepts:
     let trace: StateBuddyTrace = match from_value(js_trace) {
         Ok(trace) => trace,
-        Err(e) => return JsValue::from_str("failed to parse JSON"),
+        Err(e) => return JsValue::from_str(("failed to parse JSON: ".to_owned() + &e.to_string()).as_str()),
     };
     let mut traceMap = HashMap::<&str, Signal<f64>>::new();
     for entry in &trace.entries {