string length now supported

src/bin/bin.rs

@@ -12,7 +12,6 @@ pub fn main() {
 
     // Setup executor
     let expr = Parser::new(tokens).parse_all().unwrap();
-    print!("{:#?}", expr);
 
     let mut engine: Interpreter = Executor::new();
     let result = engine.run(&expr);

src/lib/exec.rs

@@ -95,6 +95,9 @@ impl Executor for Interpreter {
             ExprDef::ConstExpr(Const::Undefined) => Ok(Gc::new(ValueData::Undefined)),
             ExprDef::ConstExpr(Const::Num(num)) => Ok(to_value(num)),
             ExprDef::ConstExpr(Const::Int(num)) => Ok(to_value(num)),
+            // we can't move String from Const into value, because const is a garbage collected value
+            // Which means Drop() get's called on Const, but str will be gone at that point.
+            // Do Const values need to be garbage collected? We no longer need them once we've generated Values
             ExprDef::ConstExpr(Const::String(ref str)) => Ok(to_value(str.to_owned())),
             ExprDef::ConstExpr(Const::Bool(val)) => Ok(to_value(val)),
             ExprDef::ConstExpr(Const::RegExp(_, _, _)) => Ok(to_value(None::<()>)),
@@ -128,7 +131,6 @@ impl Executor for Interpreter {
             }
             ExprDef::GetConstFieldExpr(ref obj, ref field) => {
                 let val_obj = self.run(obj)?;
-                println!("{:?}", val_obj.get_field(String::from("length")));
                 Ok(val_obj.borrow().get_field(field.clone()))
             }
             ExprDef::GetFieldExpr(ref obj, ref field) => {

src/lib/js/value.rs

@@ -55,6 +55,13 @@ impl ValueData {
         Gc::new(ValueData::Object(GcCell::new(obj)))
     }
 
+    /// Similar to `new_obj`, but you can pass a prototype to create from
+    pub fn new_obj_from_prototype(proto: Value) -> Value {
+        let mut obj: ObjectData = HashMap::new();
+        obj.insert(INSTANCE_PROTOTYPE.to_string(), Property::new(proto));
+        Gc::new(ValueData::Object(GcCell::new(obj)))
+    }
+
     /// Returns true if the value is an object
     pub fn is_object(&self) -> bool {
         match *self {
@@ -152,6 +159,13 @@ impl ValueData {
     /// Resolve the property in the object
     /// Returns a copy of the Property
     pub fn get_prop(&self, field: String) -> Option<Property> {
+        // handle length
+        // Spidermonkey has its own GetLengthProperty: https://searchfox.org/mozilla-central/source/js/src/vm/Interpreter-inl.h#154
+        // TODO: Maybe we need a GetLengthProperty for value types
+        if let ValueData::String(ref s) = *self {
+            return Some(Property::new(to_value(s.len() as f64)))
+        }
+
         let obj: ObjectData = match *self {
             ValueData::Object(ref obj) => {
                 let hash = obj.clone();

tests/js/test.js

@@ -1,2 +1,2 @@
-a = { a: 1 };
-a;
+var a =  'jabra888';
+a.length;