src/java/me/topchetoeu/jscript/compilation/scope/FunctionScope.java

@@ -39,6 +39,14 @@ public class FunctionScope extends Scope {
         return childVar;
     }
 
+    @Override public boolean has(String name) {
+        if (locals.has(name)) return true;
+        if (captures.has(name)) return true;
+        if (parent != null) return parent.has(name);
+
+        return false;
+    }
+
     public int localsCount() {
         return locals.size();
     }

src/java/me/topchetoeu/jscript/compilation/scope/GlobalScope.java

@@ -15,4 +15,9 @@ public final class GlobalScope extends Scope {
     @Override public int offset() {
         return 0;
     }
+    @Override public boolean has(String name) {
+        return false;
+    }
+
+    public GlobalScope() { super(); }
 }

src/java/me/topchetoeu/jscript/compilation/scope/LocalScope.java

@@ -29,6 +29,13 @@ public class LocalScope extends Scope {
         return null;
     }
 
+    @Override public boolean has(String name) {
+        if (locals.has(name)) return true;
+        if (parent != null) return parent.has(name);
+
+        return false;
+    }
+
     @Override public boolean end() {
         if (!super.end()) return false;
 
@@ -40,6 +47,7 @@ public class LocalScope extends Scope {
         return () -> locals.iterator();
     }
 
+
     public LocalScope(Scope parent) {
         super(parent);
     }

src/java/me/topchetoeu/jscript/compilation/scope/Scope.java

@@ -35,6 +35,7 @@ public abstract class Scope {
      * which could break the semantics of a capture
      */
     public abstract VariableDescriptor get(String name, boolean capture);
+    public abstract boolean has(String name);
     /**
      * Gets the index offset from this scope to its children
      */