diff --git a/vm/src/obj/objsequence.rs b/vm/src/obj/objsequence.rs
index 893e8cd82..2fd97d279 100644
--- a/vm/src/obj/objsequence.rs
+++ b/vm/src/obj/objsequence.rs
@@ -78,6 +78,7 @@ pub trait PySliceableSequence {
                 } else if step.is_positive() {
                     let range = self.get_slice_range(start, stop);
                     if range.start < range.end {
+                        #[allow(clippy::range_plus_one)]
                         match step.to_i32() {
                             Some(1) => Ok(self.do_slice(range)),
                             Some(num) => Ok(self.do_stepped_slice(range, num as usize)),
diff --git a/wasm/lib/src/browser_module.rs b/wasm/lib/src/browser_module.rs
index 8766d06b4..e30f65391 100644
--- a/wasm/lib/src/browser_module.rs
+++ b/wasm/lib/src/browser_module.rs
@@ -75,8 +75,8 @@ fn browser_fetch(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     if let Some(headers) = headers {
         let h = request.headers();
         for (key, value) in rustpython_vm::obj::objdict::get_key_value_pairs(&headers) {
-            let ref key = vm.to_str(&key)?.value;
-            let ref value = vm.to_str(&value)?.value;
+            let key = &vm.to_str(&key)?.value;
+            let value = &vm.to_str(&value)?.value;
             h.set(key, value)
                 .map_err(|err| convert::js_py_typeerror(vm, err))?;
         }
@@ -163,9 +163,8 @@ pub struct PyPromise {
 }
 
 impl PyValue for PyPromise {
-    fn class(_vm: &mut VirtualMachine) -> PyObjectRef {
-        // TODO
-        unimplemented!()
+    fn class(vm: &mut VirtualMachine) -> PyObjectRef {
+        vm.class(BROWSER_NAME, "Promise")
     }
 }
 
@@ -183,7 +182,7 @@ pub fn get_promise_value(obj: &PyObjectRef) -> Promise {
 }
 
 pub fn import_promise_type(vm: &mut VirtualMachine) -> PyResult {
-    match import_module(vm, PathBuf::default(), BROWSER_NAME)?.get_attr("Promise".into()) {
+    match import_module(vm, PathBuf::default(), BROWSER_NAME)?.get_attr("Promise") {
         Some(promise) => Ok(promise),
         None => Err(vm.new_not_implemented_error("No Promise".to_string())),
     }
diff --git a/wasm/lib/src/convert.rs b/wasm/lib/src/convert.rs
index 42d4675f0..1cf890768 100644
--- a/wasm/lib/src/convert.rs
+++ b/wasm/lib/src/convert.rs
@@ -129,10 +129,7 @@ pub fn py_to_js(vm: &mut VirtualMachine, py_obj: PyObjectRef) -> JsValue {
         }
         arr.into()
     } else {
-        let dumps = rustpython_vm::import::import_module(vm, std::path::PathBuf::default(), "json")
-            .expect("Couldn't get json module")
-            .get_attr("dumps".into())
-            .expect("Couldn't get json dumps");
+        let dumps = vm.class("json", "dumps");
         match vm.invoke(dumps, PyFuncArgs::new(vec![py_obj], vec![])) {
             Ok(value) => {
                 let json = vm.to_pystr(&value).unwrap();
@@ -156,7 +153,7 @@ pub fn object_entries(obj: &Object) -> impl Iterator<Item = Result<(JsValue, JsV
 pub fn pyresult_to_jsresult(vm: &mut VirtualMachine, result: PyResult) -> Result<JsValue, JsValue> {
     result
         .map(|value| py_to_js(vm, value))
-        .map_err(|err| py_err_to_js_err(vm, &err).into())
+        .map_err(|err| py_err_to_js_err(vm, &err))
 }
 
 pub fn js_to_py(vm: &mut VirtualMachine, js_val: JsValue) -> PyObjectRef {
@@ -229,11 +226,7 @@ pub fn js_to_py(vm: &mut VirtualMachine, js_val: JsValue) -> PyObjectRef {
         // Because `JSON.stringify(undefined)` returns undefined
         vm.get_none()
     } else {
-        let loads = rustpython_vm::import::import_module(vm, std::path::PathBuf::default(), "json")
-            .expect("Couldn't get json module")
-            .get_attr("loads".into())
-            .expect("Couldn't get json dumps");
-
+        let loads = vm.class("json", "dumps");
         let json = match js_sys::JSON::stringify(&js_val) {
             Ok(json) => String::from(json),
             Err(_) => return vm.get_none(),
diff --git a/wasm/lib/src/vm_class.rs b/wasm/lib/src/vm_class.rs
index dfca86f52..408e2b3cc 100644
--- a/wasm/lib/src/vm_class.rs
+++ b/wasm/lib/src/vm_class.rs
@@ -3,7 +3,7 @@ use std::collections::HashMap;
 use std::rc::{Rc, Weak};
 
 use js_sys::{Object, Reflect, SyntaxError, TypeError};
-use wasm_bindgen::{prelude::*, JsCast};
+use wasm_bindgen::prelude::*;
 
 use rustpython_vm::compile;
 use rustpython_vm::frame::{NameProtocol, Scope};