diff --git a/hscript/Error.hx b/hscript/Error.hx
index 5c8cdd5..5fafa8a 100644
--- a/hscript/Error.hx
+++ b/hscript/Error.hx
@@ -51,6 +51,7 @@ enum Error
 	EInvalidPreprocessor( msg : String );
 	EUnknownVariable( v : String );
 	EInvalidIterator( v : String );
+	EInvalidType( t : String );
 	EInvalidOp( op : String );
 	EInvalidAccess( f : String );
 	ECustom( msg : String );
diff --git a/hscript/Interp.hx b/hscript/Interp.hx
index e89b025..ff3530c 100644
--- a/hscript/Interp.hx
+++ b/hscript/Interp.hx
@@ -159,6 +159,7 @@ class Interp {
 		variables.set("true", true);
 		variables.set("false", false);
 		#if !NO_FROM_CHAR_CODE_FIX
+		// DONT CALL THIS DIRECTLY, USE String.fromCharCode, the preprocessor will call it for you
 		variables.set("__StringWorkaround__fromCharCode", function(a:Int) { // TODO: make hscript only add this if its used
 			return String.fromCharCode(a);
 		});
diff --git a/hscript/Optimizer.hx b/hscript/Optimizer.hx
index 8e9e234..6d3879f 100644
--- a/hscript/Optimizer.hx
+++ b/hscript/Optimizer.hx
@@ -6,6 +6,8 @@ import hscript.Parser;
 
 @:access(hscript.Parser)
 class Optimizer {
+	static inline function expr(e:Expr) return Tools.expr(e);
+
 	public static function optimize(s:Expr):Expr {
 		if(s == null)
 			return null;
@@ -54,8 +56,8 @@ class Optimizer {
 				var econd = optimize(econd);
 				var e1 = optimize(e1);
 				var e2 = optimize(e2);
-				if(isConstant(econd)) {
-					var econd = getConstant(econd);
+				if(isBool(econd)) {
+					var econd = getBool(econd);
 					if(econd == true) {
 						if(e1 == null)
 							return mk(EBlock([]), s);
@@ -66,6 +68,27 @@ class Optimizer {
 						return mk(EBlock([e2]), s);
 					}
 				}
+				if(e2 != null && isBool(e1) && isBool(e2)) {
+					var c1 = getBool(e1);
+					var c2 = getBool(e2);
+
+					if(c1 == false && c2 == true) { // (VAR ? false : true)
+						return optimize(mk(EUnop("!", true, econd), s));
+					}
+					if(c1 == true && c2 == false) { // (VAR ? true : false)
+						return optimize(mk(Tools.expr(econd), s));
+					}
+					if(isConstant(econd)) { // Side effect free
+						if(c1 == true && c2 == true) { // (CONST ? true : true)
+							return mk(convertConstant(true), s);
+						}
+						if(c1 == false && c2 == false) { // (CONST ? false : false)
+							return mk(convertConstant(false), s);
+						}
+						// TODO: Check if local variables are used in the condition
+						// Since they cant have side effects, they can be optimized
+					}
+				}
 				return mk(EIf(econd, e1, e2), s);
 
 			case ETernary(econd, e1, e2):
@@ -94,7 +117,7 @@ class Optimizer {
 					if(c1 == true && c2 == false) { // (VAR ? true : false)
 						return optimize(mk(Tools.expr(econd), s));
 					}
-					if(isConstant(econd)) {
+					if(isConstant(econd)) { // Side effect free
 						if(c1 == true && c2 == true) { // (CONST ? true : true)
 							return mk(convertConstant(true), s);
 						}
@@ -146,23 +169,86 @@ class Optimizer {
 			case ECall(e, params):
 				e = optimize(e);
 				params = params.map((v) -> optimize(v));
-				if(params.length == 0) {
-					switch(Tools.expr(e)) {
-						case EField(fc, "toUpperCase", _):
-							var str = getStringConstant(fc);
-							if(str != null)
-								return mk(convertConstant(str.toUpperCase()), s);
-						case EField(fc, "toLowerCase", _):
-							var str = getStringConstant(fc);
-							if(str != null)
-								return mk(convertConstant(str.toLowerCase()), s);
-						default:
+
+				function p(i:Int, t:ConstType, opt:Bool = false):Dynamic {
+					var p = params[i];
+					if(t != getConstType(p))
+						if(opt)
+							return null;
+						else
+							throw Parser.getBaseError(EInvalidType(getTypeName(p)));
+					return switch(t) {
+						case CTInt: getInt(p);
+						case CTFloat: getFloat(p);
+						case CTBool: getBool(p);
+						case CTString: getStringConstant(p);
+						case CTNull: null;
 					}
 				}
+
+				switch(Tools.expr(e)) {
+					case EField(expr(_) => EConst(CString(str)), field):
+						switch(field) {
+							case "toString":
+								if(params.length != 0) throw Parser.getBaseError(ECustom("String.toString() takes no arguments"));
+								return mk(convertConstant(str.toString()), s);
+
+							case "toUpperCase":
+								if(params.length != 0) throw Parser.getBaseError(ECustom("String.toUpperCase() takes no arguments"));
+								return mk(convertConstant(str.toUpperCase()), s);
+
+							case "toLowerCase":
+								if(params.length != 0) throw Parser.getBaseError(ECustom("String.toLowerCase() takes no arguments"));
+								return mk(convertConstant(str.toLowerCase()), s);
+
+							case "charAt":
+								var index = p(0, CTInt);
+								return mk(convertConstant(str.charAt(index)), s);
+
+							case "charCodeAt":
+								var index = p(0, CTInt);
+								return mk(convertConstant(str.charCodeAt(index)), s);
+
+							case "indexOf":
+								var value = p(0, CTString);
+								var startIndex = p(1, CTInt, true);
+								return mk(convertConstant(str.indexOf(value, startIndex)), s);
+
+							case "lastIndexOf":
+								var value = p(0, CTString);
+								var startIndex = p(1, CTInt, true);
+								return mk(convertConstant(str.lastIndexOf(value, startIndex)), s);
+
+							case "split":
+								var delimiter = p(0, CTString);
+								var strArr = str == "" ? [] : str.split(delimiter); // fix platform dependent behavior
+								return mk(EArrayDecl([for(st in strArr) mk(EConst(CString(st)), s)]), s);
+
+							case "substr":
+								var pos = p(0, CTInt);
+								var len = p(1, CTInt, true);
+								return mk(convertConstant(str.substr(pos, len)), s);
+
+							case "substring":
+								var startIndex = p(0, CTInt);
+								var endIndex = p(1, CTInt, true);
+								return mk(convertConstant(str.substring(startIndex, endIndex)), s);
+						}
+						default:
+				}
+				switch(Tools.expr(e)) {
+
+					default:
+				}
 				return mk(ECall(e, params), s);
 
 			case EField(e, f, safe):
 				e = optimize(e);
+				switch(Tools.expr(e)) {
+					case EConst(CString(str)) if(f == "length"):
+						return mk(convertConstant(str.length), s);
+					default:
+				}
 				return mk(EField(e, f, safe), s);
 
 			case EIdent(_) | EConst(_):
@@ -226,6 +312,7 @@ class Optimizer {
 						}
 					}
 
+					// Maybe convert this to a Lambda.foreach?
 					var isAllCasesConstant = true;
 					for(c in cases) {
 						for(v in c.values) {
@@ -268,19 +355,23 @@ class Optimizer {
 						};
 
 						var constant = Lambda.exists(arr, isConstant);
-						if(constant) {
-							return mk(Tools.expr(arr[getConstant(index)]), s);
+						var index = getInt(index);
+						if(constant && index != null) {
+							return mk(Tools.expr(arr[index]), s);
 						}
 					}
 					if(Tools.expr(e).match(EMapDecl(_))) {
 						var map = switch(Tools.expr(e)) {
-							case EMapDecl(type, keys, vals): [keys, vals];
+							case EMapDecl(type, keys, vals): [for(i in 0...keys.length) [keys[i], vals[i]]];
 							default: null;
 						};
 
 						var constant = Lambda.exists(map, (v) -> isConstant(v[0]) && isConstant(v[1]));
 						if(constant) {
-							return mk(Tools.expr(map[getConstant(index)][1]), s);
+							var idx = Lambda.findIndex(map, (v) -> Type.enumEq(Tools.expr(v[0]), Tools.expr(index)));
+							if(idx == -1)
+								return mk(EIdent("null"), s);
+							return mk(Tools.expr(map[idx][1]), s);
 						}
 					}
 				}
@@ -301,6 +392,8 @@ class Optimizer {
 					var c1 = getNumber(e1);
 					if(compareNumber(c1, 0) && op == "+")
 						return mk(Tools.expr(e2), s);
+					if(compareNumber(c1, 1) && op == "*")
+						return mk(Tools.expr(e2), s);
 					//if(compareNumber(c1, 0) && op == "*")
 					//	return mk(convertConstant(0), s);
 				}
@@ -311,6 +404,8 @@ class Optimizer {
 						return mk(Tools.expr(e1), s);
 					if(op == "/" && compareNumber(c2, 1))
 						return mk(Tools.expr(e1), s);
+					if(op == "*" && compareNumber(c2, 1))
+						return mk(Tools.expr(e1), s);
 					//if(op == "*" && compareNumber(c2, 0))
 					//	return mk(convertConstant(0), s);
 				}
@@ -366,6 +461,35 @@ class Optimizer {
 		}
 	}
 
+	static function getTypeName(e:Expr):String {
+		if(e == null)
+			return null;
+		return switch(Tools.expr(e)) {
+			case EConst(CInt(_)): "Int";
+			case EConst(CFloat(_)): "Float";
+			case EConst(CString(_)): "String";
+			case EIdent("true") | EIdent("false"): "Bool";
+			case EIdent("null"): "Null";
+			case EIdent(_): "Dynamic";
+			case EParent(e): getTypeName(e);
+			default: Std.string(Tools.expr(e));
+		}
+	}
+
+	static function getConstType(e:Expr):ConstType {
+		if(e == null)
+			return null;
+		return switch(Tools.expr(e)) {
+			case EConst(CInt(_)): CTInt;
+			case EConst(CFloat(_)): CTFloat;
+			case EConst(CString(_)): CTString;
+			case EIdent("true") | EIdent("false"): CTBool;
+			case EIdent("null"): CTNull;
+			case EParent(e): getConstType(e);
+			default: throw "Unknown type " + Tools.expr(e);
+		}
+	}
+
 	static function isConstant(e:Expr):Bool {
 		return switch(Tools.expr(e)) {
 			case EIdent("true") | EIdent("false") | EIdent("null"): true;
@@ -404,15 +528,44 @@ class Optimizer {
 	static function getBool(e:Expr):Bool {
 		return switch(Tools.expr(e)) {
 			case EIdent("true"): true;
-			case EIdent("false"): true;
+			case EIdent("false"): false;
 			case EParent(e): getBool(e);
 			default: throw "Unknown type " + Tools.expr(e);
 		}
 	}
 
+	static function getInt(e:Expr):Null<Int> {
+		if(e == null)
+			return null;
+		return switch(Tools.expr(e)) {
+			case EConst(CInt(value)): value;
+			case EParent(e): getInt(e);
+			default: null;
+		}
+	}
+
+	static function getFloat(e:Expr):Null<Float> {
+		if(e == null)
+			return null;
+		return switch(Tools.expr(e)) {
+			case EConst(CFloat(value)): value;
+			case EParent(e): getFloat(e);
+			default: null;
+		}
+	}
+
+	static function isString(e:Expr):Bool {
+		return switch(Tools.expr(e)) {
+			case EConst(CString(_)): true;
+			case EParent(e): isString(e);
+			default: false;
+		}
+	}
+
 	static function getStringConstant(e:Expr):String {
 		return switch(Tools.expr(e)) {
 			case EConst(CString(value)): value;
+			case EParent(e): getStringConstant(e);
 			default: null;
 		}
 	}
@@ -476,4 +629,12 @@ class Optimizer {
 			default: null;
 		}
 	}
+}
+
+enum ConstType {
+	CTInt;
+	CTFloat;
+	CTBool;
+	CTString;
+	CTNull;
 }
\ No newline at end of file
diff --git a/hscript/Printer.hx b/hscript/Printer.hx
index 47212e7..011f8ab 100644
--- a/hscript/Printer.hx
+++ b/hscript/Printer.hx
@@ -537,6 +537,7 @@ class Printer {
 			case EInvalidPreprocessor(str): "Invalid preprocessor (" + str + ")";
 			case EUnknownVariable(v): "Unknown variable: "+v;
 			case EInvalidIterator(v): "Invalid iterator: "+v;
+			case EInvalidType(t): "Invalid type: "+t;
 			case EInvalidOp(op): "Invalid operator: "+op;
 			case EInvalidAccess(f): "Invalid access to field " + f;
 			case ECustom(msg): msg;
diff --git a/tests/src/Util.hx b/tests/src/Util.hx
index 095a546..2cb2f60 100644
--- a/tests/src/Util.hx
+++ b/tests/src/Util.hx
@@ -37,10 +37,10 @@ class Util {
 				var b_args = EnumValueTools.getParameters(cast b);
 				return deepEqual(a_args, b_args);
 			case TClass(_):
-				if (Std.isOfType(a, String) && Std.isOfType(b, String)) {
+				if ((a is String) && (b is String)) {
 					return a == b;
 				}
-				if (Std.isOfType(a, Array) && Std.isOfType(b, Array)) {
+				if ((a is Array) && (b is Array)) {
 					var a = cast(a, Array<Dynamic>);
 					var b = cast(b, Array<Dynamic>);
 					if (a.length != b.length) { return false; }
@@ -52,9 +52,9 @@ class Util {
 					return true;
 				}
 
-				if (Std.isOfType(a, IMap) && Std.isOfType(b, IMap)) {
-					var a = cast(a, Map<Dynamic, Dynamic>);
-					var b = cast(b, Map<Dynamic, Dynamic>);
+				if ((a is IMap) && (b is IMap)) {
+					var a = cast(a, IMap<Dynamic, Dynamic>);
+					var b = cast(b, IMap<Dynamic, Dynamic>);
 					var a_keys = [ for (key in a.keys()) key ];
 					var b_keys = [ for (key in b.keys()) key ];
 					a_keys.sort(Reflect.compare);
@@ -68,11 +68,11 @@ class Util {
 					return true;
 				}
 
-				if (Std.isOfType(a, Date) && Std.isOfType(b, Date)) {
+				if ((a is Date) && (b is Date)) {
 					return cast(a, Date).getTime() == cast(b, Date).getTime();
 				}
 
-				if (Std.isOfType(a, haxe.io.Bytes) && Std.isOfType(b, haxe.io.Bytes)) {
+				if ((a is haxe.io.Bytes) && (b is haxe.io.Bytes)) {
 					return deepEqual(cast(a, haxe.io.Bytes).getData(), cast(b, haxe.io.Bytes).getData());
 				}
 
diff --git a/tests/src/tests/FinalCase.hx b/tests/src/tests/FinalCase.hx
index f1e0623..825758c 100644
--- a/tests/src/tests/FinalCase.hx
+++ b/tests/src/tests/FinalCase.hx
@@ -83,6 +83,7 @@ class FinalCase extends TestCase {
 
 		assertEq("[0=>'hello', 1=>'world']", [0=>'hello', 1=>'world']);
 		assertEq("[0=>'hello', 1=>'world'][1]", [0=>'hello', 1=>'world'][1]);
+		assertEq("[0=>'hello', 5=>'world'][1]", [0=>'hello', 5=>'world'][1]);
 
 		// Test EOF with preprocessor
 	}
diff --git a/tests/src/tests/StringCase.hx b/tests/src/tests/StringCase.hx
index c9c60c1..ca6cbd7 100644
--- a/tests/src/tests/StringCase.hx
+++ b/tests/src/tests/StringCase.hx
@@ -151,15 +151,27 @@ class StringCase extends TestCase {
 		assertEq('String.fromCharCode(101)', String.fromCharCode(101));
 		assertEq('String.fromCharCode(102)', String.fromCharCode(102));
 		assertEq('String.fromCharCode(103)', String.fromCharCode(103));
-		assertEq('var a = 103; String.fromCharCode(a)', String.fromCharCode(test));
+		assertEq('var a = 103; String.fromCharCode(a)', String.fromCharCode(a));
 
 		assertError("'hello ${}'", Parser.getBaseError(EPreset(EMPTY_INTERPOLATION)));
-	}
 
-	static var test = 103;
+		assertEq('"".charAt(0)', "".charAt(0));
+		assertEq('"".charAt(1)', "".charAt(1));
+		assertEq('"".charAt(-1)', "".charAt(-1));
 
-	static function fromCharCode(a:Int) {
-		return String.fromCharCode(a);
+		headerCode = '';
+
+		assertEq("'foo1bar'.charCodeAt(0)", 'foo1bar'.charCodeAt(0));
+		assertEq("'foo1bar'.charCodeAt(1)", 'foo1bar'.charCodeAt(1));
+		assertEq("'foo1bar'.charCodeAt(2)", 'foo1bar'.charCodeAt(2));
+		assertEq("'foo1bar'.charCodeAt(3)", 'foo1bar'.charCodeAt(3));
+		assertEq("'foo1bar'.charCodeAt(4)", 'foo1bar'.charCodeAt(4));
+		assertEq("'foo1bar'.charCodeAt(5)", 'foo1bar'.charCodeAt(5));
+		assertEq("'foo1bar'.charCodeAt(6)", 'foo1bar'.charCodeAt(6));
+		assertEq("'foo1bar'.charCodeAt(7)", 'foo1bar'.charCodeAt(7));
+		assertEq("'foo1bar'.charCodeAt(-1)", 'foo1bar'.charCodeAt(-1));
+		assertEq("'foo1bar'.length", 'foo1bar'.length);
+		assertEq("'foo1bar'.split('1')", 'foo1bar'.split('1'));
 	}
 
 	override function teardown() {