unassigned var is undefined

.gitignore

@@ -2,11 +2,18 @@
 .idea/
 *.iml
 
+# Vim
+.*.swp
+.*.swo
+
 # Build
 target
 dist
 **/*.rs.bk
 node_modules
 .DS_Store
 yarn-error.log
-.vscode/settings.json
+.vscode/settings.json
+
+# tests/js/test.js is used for testing changes locally
+test/js/test.js

CHANGELOG.md

@@ -15,6 +15,11 @@ Feature enhancements:
 - [FEATURE #119](https://github.com/jasonwilliams/boa/issues/119):
   Introduce realm struct to hold realm context and global object
 
+Bug fixes:
+
+- [BUG #113](https://github.com/jasonwilliams/boa/issues/113):
+  Unassigned variables have default of undefined (@pop)
+
 # 0.4.0 (2019-09-25)
 
 v0.4.0 brings quite a big release. The biggest feature to land is the support of regular expressions.  

src/lib/exec.rs

@@ -389,7 +389,7 @@ impl Executor for Interpreter {
                     let (name, value) = var.clone();
                     let val = match value {
                         Some(v) => self.run(&v)?,
-                        None => Gc::new(ValueData::Null),
+                        None => Gc::new(ValueData::Undefined),
                     };
                     self.realm
                         .environment
@@ -403,7 +403,7 @@ impl Executor for Interpreter {
                     let (name, value) = var.clone();
                     let val = match value {
                         Some(v) => self.run(&v)?,
-                        None => Gc::new(ValueData::Null),
+                        None => Gc::new(ValueData::Undefined),
                     };
                     self.realm
                         .environment
@@ -630,3 +630,32 @@ impl Interpreter {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::exec;
+
+    #[test]
+    fn empty_let_decl_undefined() {
+        let scenario = r#"
+        let a;
+        a == undefined;
+        "#;
+
+        let pass = String::from("true");
+
+        assert_eq!(exec(scenario), pass);
+    }
+
+    #[test]
+    fn empty_var_decl_undefined() {
+        let scenario = r#"
+        let b;
+        b == undefined;
+        "#;
+
+        let pass = String::from("true");
+
+        assert_eq!(exec(scenario), pass);
+    }
+}

tests/js/test.js

@@ -1,2 +1,6 @@
+///
+// Use this file to test your changes to boa.
+///
+
 let a = Boolean(0);
 typeof a;