Prevent DefVar opcode emit for global binding

boa_engine/src/bytecompiler/mod.rs

@@ -407,8 +407,10 @@ impl<'ctx, 'host> ByteCompiler<'ctx, 'host> {
         match opcode {
             BindingOpcode::Var => {
                 let binding = self.variable_environment.get_identifier_reference(name);
-                let index = self.get_or_insert_binding(binding.locator());
-                self.emit_with_varying_operand(Opcode::DefVar, index);
+                if !binding.locator().is_global() {
+                    let index = self.get_or_insert_binding(binding.locator());
+                    self.emit_with_varying_operand(Opcode::DefVar, index);
+                }
             }
             BindingOpcode::InitVar => match self.lexical_environment.set_mutable_binding(name) {
                 Ok(binding) => {

boa_engine/src/vm/opcode/define/mod.rs

@@ -22,15 +22,11 @@ impl DefVar {
         // TODO: spec specifies to return `empty` on empty vars, but we're trying to initialize.
         let binding_locator = context.vm.frame().code_block.bindings[index];
 
-        if binding_locator.is_global() {
-            // already initialized at compile time
-        } else {
-            context.vm.environments.put_value_if_uninitialized(
-                binding_locator.environment_index(),
-                binding_locator.binding_index(),
-                JsValue::undefined(),
-            );
-        }
+        context.vm.environments.put_value_if_uninitialized(
+            binding_locator.environment_index(),
+            binding_locator.binding_index(),
+            JsValue::undefined(),
+        );
         Ok(CompletionType::Normal)
     }
 }