make arguments null prototype, to follow spec closer

runtime/src/main/java/me/topchetoeu/j2s/runtime/ArgumentsValue.java

@@ -1,13 +1,53 @@
 package me.topchetoeu.j2s.runtime;
 
+import me.topchetoeu.j2s.common.Environment;
 import me.topchetoeu.j2s.runtime.values.Value;
-import me.topchetoeu.j2s.runtime.values.objects.ArrayValue;
+import me.topchetoeu.j2s.runtime.values.objects.ArrayLikeValue;
 
-public class ArgumentsValue extends ArrayValue {
+public class ArgumentsValue extends ArrayLikeValue {
 	public final Frame frame;
+	private Value[] args;
+	private boolean shadowed;
 
-	public ArgumentsValue(Frame frame, Value... args) {
+	private void shadow() {
-		super(args);
+		if (!shadowed) {
+			var newArgs = new Value[args.length];
+			System.arraycopy(args, 0, newArgs, 0, args.length);
+			args = newArgs;
+			shadowed = true;
+		}
+	}
+
+	@Override public Value get(int i) {
+		return args[i];
+	}
+	@Override public boolean has(int i) {
+		if (i < 0 || i >= size()) return false;
+
+		if (shadowed) return args[i] != null;
+		else return true;
+	}
+	@Override public boolean remove(int i) {
+		shadow();
+		args[i] = null;
+		return true;
+	}
+	@Override public boolean set(Environment env, int i, Value val) {
+		shadow();
+		args[i] = val;
+		return true;
+	}
+	@Override public boolean setSize(int val) {
+		return false;
+	}
+	@Override public int size() {
+		return args.length;
+	}
+
+	public ArgumentsValue(Frame frame) {
 		this.frame = frame;
+		this.args = frame.args;
+		this.shadowed = false;
+		setPrototype(e -> null);
 	}
 }

runtime/src/main/java/me/topchetoeu/j2s/runtime/Frame.java

@@ -383,7 +383,7 @@ public final class Frame {
 
 		this.self = self;
 		this.args = args;
-		this.argsVal = new ArgumentsValue(this, args);
+		this.argsVal = new ArgumentsValue(this);
 		this.argsLen = new IntValue(args.length);
 		this.captures = func.captures;
 

runtime/src/main/java/me/topchetoeu/j2s/runtime/values/objects/ArrayLikeValue.java

@@ -56,6 +56,17 @@ public abstract class ArrayLikeValue extends ObjectValue {
 	public abstract boolean has(int i);
 	public abstract boolean remove(int i);
 
+	public Value[] toArray() {
+		var n = size();
+		var res = new Value[n];
+
+		for (var i = 0; i < n; i++) {
+			if (has(i)) res[i] = get(i);
+		}
+
+		return res;
+	}
+
 	@Override public Member getOwnMember(Environment env, KeyCache key) {
 		var res = super.getOwnMember(env, key);
 		if (res != null) return res;

runtime/src/main/java/me/topchetoeu/j2s/runtime/values/objects/ArrayValue.java

@@ -68,7 +68,7 @@ public class ArrayValue extends ArrayLikeValue implements Iterable<Value> {
 		}
 	}
 
-	public Value[] toArray() {
+	@Override public Value[] toArray() {
 		var res = new Value[size];
 		copyTo(res, 0, 0, size);
 		return res;