Handle undefined as a constant

valuescript_compiler/src/constants.rs

@@ -1,6 +1,7 @@
 use crate::asm::{Number, Value};
 
-pub const CONSTANTS: [(&'static str, Value); 2] = [
+pub const CONSTANTS: [(&str, Value); 3] = [
+  ("undefined", Value::Undefined),
   ("NaN", Value::Number(Number(std::f64::NAN))),
   ("Infinity", Value::Number(Number(std::f64::INFINITY))),
 ];

valuescript_compiler/src/expression_compiler.rs

@@ -1282,11 +1282,6 @@ impl<'a> ExpressionCompiler<'a> {
     ident: &swc_ecma_ast::Ident,
     target_register: Option<Register>,
   ) -> CompiledExpression {
-    // TODO: Use constant instead?
-    if ident.sym.to_string() == "undefined" {
-      return Value::Undefined.to_ce();
-    }
-
     let fn_as_owner_id = match self.fnc.scope_analysis.lookup(ident) {
       Some(name) => match name.type_ == NameType::Function {
         true => match name.id {

valuescript_compiler/src/scope_analysis.rs

@@ -1584,13 +1584,6 @@ impl ScopeAnalysis {
   }
 
   fn ident(&mut self, scope: &Scope, ident: &swc_ecma_ast::Ident) {
-    if ident.sym.to_string() == "undefined" {
-      // The way that `undefined` is considered to be an identifier is an artifact of history. It's
-      // not an identifier (unless used in an identifier context like an object key), instead it's a
-      // keyword like `null`.
-      return;
-    }
-
     let name_id = match scope.get(&ident.sym) {
       Some(name_id) => name_id,
       None => {