diff --git a/vlib/builtin/js/array.js.v b/vlib/builtin/js/array.js.v
index ac0f2321a1..495e656db1 100644
--- a/vlib/builtin/js/array.js.v
+++ b/vlib/builtin/js/array.js.v
@@ -136,7 +136,7 @@ pub fn (a array) str() string {
 }
 
 #array.prototype[Symbol.iterator] = function () { return this.arr[Symbol.iterator](); }
-#array.prototype.entries = function () { return this.arr.entries(); }
+#array.prototype.entries = function () { let result = []; for (const [key,val] of this.arr.entries()) { result.push([new int(key), val]); } return result[Symbol.iterator](); }
 #array.prototype.map = function(callback) { return new builtin.array(this.arr.map(callback)); }
 #array.prototype.filter = function(callback) { return new array(this.arr.filter( function (it) { return (+callback(it)) != 0; } )); }
 #Object.defineProperty(array.prototype,'cap',{ get: function () { return this.len; } })
diff --git a/vlib/builtin/js/builtin.js.v b/vlib/builtin/js/builtin.js.v
index 80654160ad..f64da0070c 100644
--- a/vlib/builtin/js/builtin.js.v
+++ b/vlib/builtin/js/builtin.js.v
@@ -2,36 +2,36 @@ module builtin
 
 // used to generate JS throw statements.
 pub fn js_throw(s any) {
-	#throw (s instanceof Error ? s : new Error(s))
+	#throw s
 }
 
-pub fn println(s any) {
+pub fn println(s string) {
 	$if js_freestanding {
-		#print(s.toString())
+		#print(s.str)
 	} $else {
-		#console.log(s.toString())
+		#console.log(s.str)
 	}
 }
 
-pub fn print(s any) {
+pub fn print(s string) {
 	$if js_node {
-		#$process.stdout.write(s.toString())
+		#$process.stdout.write(s.str)
 	} $else {
 		panic('Cannot `print` in a browser, use `println` instead')
 	}
 }
 
-pub fn eprintln(s any) {
+pub fn eprintln(s string) {
 	$if js_freestanding {
-		#print(s.toString())
+		#print(s.str)
 	} $else {
-		#console.error(s.toString())
+		#console.error(s.str)
 	}
 }
 
-pub fn eprint(s any) {
+pub fn eprint(s string) {
 	$if js_node {
-		#$process.stderr.write(s.toString())
+		#$process.stderr.write(s.str)
 	} $else {
 		panic('Cannot `eprint` in a browser, use `println` instead')
 	}
@@ -50,3 +50,12 @@ fn opt_ok(data voidptr, option Option) {
 	#option.err = none__
 	#option.data = data
 }
+
+pub fn unwrap(opt string) string {
+	mut o := Option{}
+	#o = opt
+	if o.state != 0 {
+		js_throw(o.err)
+	}
+	return opt
+}
diff --git a/vlib/builtin/js/builtin.v b/vlib/builtin/js/builtin.v
index 71e42c65f1..7c82d1ad98 100644
--- a/vlib/builtin/js/builtin.v
+++ b/vlib/builtin/js/builtin.v
@@ -6,14 +6,6 @@ module builtin
 
 fn (a any) toString()
 
-pub fn unwrap(opt any) any {
-	o := &Option(opt)
-	if o.state != 0 {
-		js_throw(o.err)
-	}
-	return opt
-}
-
 pub fn panic(s string) {
 	eprintln('V panic: $s')
 	exit(1)
@@ -32,13 +24,6 @@ pub:
 	code int
 }
 
-pub const none__ = IError(&None__{})
-
-pub struct Option {
-	state byte
-	err   IError = none__
-}
-
 struct None__ {
 	msg  string
 	code int
@@ -48,6 +33,13 @@ fn (_ None__) str() string {
 	return 'none'
 }
 
+pub const none__ = IError(None__{'', 0})
+
+pub struct Option {
+	state byte
+	err   IError = none__
+}
+
 pub fn (err IError) str() string {
 	return match err {
 		None__ { 'none' }
diff --git a/vlib/v/gen/js/fn.v b/vlib/v/gen/js/fn.v
new file mode 100644
index 0000000000..6bde0a13dd
--- /dev/null
+++ b/vlib/v/gen/js/fn.v
@@ -0,0 +1,241 @@
+module js
+
+import v.ast
+
+fn (mut g JsGen) gen_method_call(it ast.CallExpr) bool {
+	g.call_stack << it
+
+	mut name := g.js_name(it.name)
+	call_return_is_optional := it.return_type.has_flag(.optional)
+	if call_return_is_optional {
+		g.writeln('(function(){')
+		g.inc_indent()
+		g.writeln('try {')
+		g.inc_indent()
+		g.write('return builtin.unwrap(')
+	}
+	sym := g.table.get_type_symbol(it.receiver_type)
+	if sym.kind == .array {
+		if sym.kind == .array && it.name in ['map', 'filter'] {
+			g.expr(it.left)
+			mut ltyp := it.left_type
+			for ltyp.is_ptr() {
+				g.write('.val')
+				ltyp = ltyp.deref()
+			}
+			g.write('.')
+			// Prevent 'it' from getting shadowed inside the match
+			node := it
+			g.write(it.name)
+			g.write('(')
+			expr := node.args[0].expr
+			match expr {
+				ast.AnonFn {
+					g.gen_fn_decl(expr.decl)
+					g.write(')')
+					return true
+				}
+				ast.Ident {
+					if expr.kind == .function {
+						g.write(g.js_name(expr.name))
+						g.write(')')
+						return true
+					} else if expr.kind == .variable {
+						v_sym := g.table.get_type_symbol(expr.var_info().typ)
+						if v_sym.kind == .function {
+							g.write(g.js_name(expr.name))
+							g.write(')')
+							return true
+						}
+					}
+				}
+				else {}
+			}
+
+			g.write('it => ')
+			g.expr(node.args[0].expr)
+			g.write(')')
+			return true
+		}
+
+		left_sym := g.table.get_type_symbol(it.left_type)
+		if left_sym.kind == .array {
+			if it.name in special_array_methods {
+				g.expr(it.left)
+				mut ltyp := it.left_type
+				for ltyp.is_ptr() {
+					g.write('.val')
+					ltyp = ltyp.deref()
+				}
+				g.write('.')
+
+				g.gen_array_method_call(it)
+				return true
+			}
+		}
+	}
+
+	mut ltyp := it.left_type
+	mut lsym := g.table.get_type_symbol(ltyp)
+	if lsym.kind == .interface_ {
+		g.write(g.js_name(lsym.name))
+		g.write('.${name}.call(')
+		g.expr(it.left)
+		g.write(',')
+		for i, arg in it.args {
+			g.expr(arg.expr)
+			if i != it.args.len - 1 {
+				g.write(', ')
+			}
+		}
+		// end method call
+		g.write(')')
+	} else {
+		g.write('Object.getPrototypeOf(')
+		g.expr(it.left)
+
+		for ltyp.is_ptr() {
+			g.write('.val')
+			ltyp = ltyp.deref()
+		}
+		g.write(').$name .call(')
+		g.expr(it.left)
+		g.write(',')
+		for i, arg in it.args {
+			g.expr(arg.expr)
+			if i != it.args.len - 1 {
+				g.write(', ')
+			}
+		}
+		// end method call
+		g.write(')')
+	}
+
+	if call_return_is_optional {
+		// end unwrap
+		g.writeln(')')
+		g.dec_indent()
+		// begin catch block
+		g.writeln('} catch(err) {')
+		g.inc_indent()
+		// gen or block contents
+		match it.or_block.kind {
+			.block {
+				if it.or_block.stmts.len > 1 {
+					g.stmts(it.or_block.stmts[..it.or_block.stmts.len - 1])
+				}
+				// g.write('return ')
+				g.stmt(it.or_block.stmts.last())
+			}
+			.propagate {
+				panicstr := '`optional not set (\${err})`'
+				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
+					g.writeln('return builtin.panic($panicstr)')
+				} else {
+					g.writeln('builtin.js_throw(err)')
+				}
+			}
+			else {}
+		}
+		// end catch
+		g.dec_indent()
+		g.writeln('}')
+		// end anon fn
+		g.dec_indent()
+		g.write('})()')
+	}
+	g.call_stack.delete_last()
+	return true
+}
+
+fn (mut g JsGen) gen_call_expr(it ast.CallExpr) {
+	if it.is_method {
+		if g.gen_method_call(it) {
+			return
+		}
+	}
+	node := it
+	g.call_stack << it
+	mut name := g.js_name(it.name)
+	is_print := name in ['print', 'println', 'eprint', 'eprintln', 'panic']
+	print_method := name
+	ret_sym := g.table.get_type_symbol(it.return_type)
+	if it.language == .js && ret_sym.name in v_types && ret_sym.name != 'void' {
+		g.write('new ')
+		if g.ns.name != 'builtin' {
+			g.write('builtin.')
+		}
+		g.write(ret_sym.name)
+		g.write('(')
+	}
+	call_return_is_optional := it.return_type.has_flag(.optional)
+	if call_return_is_optional {
+		g.writeln('(function(){')
+		g.inc_indent()
+		g.writeln('try {')
+		g.inc_indent()
+		g.write('return builtin.unwrap(')
+	}
+	if is_print {
+		mut typ := node.args[0].typ
+
+		expr := node.args[0].expr
+		g.write('builtin.$print_method (')
+		g.gen_expr_to_string(expr, typ)
+		g.write(')')
+		return
+	}
+	g.expr(it.left)
+
+	if name in g.builtin_fns {
+		g.write('builtin.')
+	}
+
+	g.write('${name}(')
+	for i, arg in it.args {
+		g.expr(arg.expr)
+		if i != it.args.len - 1 {
+			g.write(', ')
+		}
+	}
+	// end method call
+	g.write(')')
+	if call_return_is_optional {
+		// end unwrap
+		g.writeln(')')
+		g.dec_indent()
+		// begin catch block
+		g.writeln('} catch(err) {')
+		g.inc_indent()
+		// gen or block contents
+		match it.or_block.kind {
+			.block {
+				if it.or_block.stmts.len > 1 {
+					g.stmts(it.or_block.stmts[..it.or_block.stmts.len - 1])
+				}
+
+				//	g.write('return ')
+				g.stmt(it.or_block.stmts.last())
+			}
+			.propagate {
+				panicstr := '`optional not set (\${err})`'
+				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
+					g.writeln('return builtin.panic($panicstr)')
+				} else {
+					g.writeln('builtin.js_throw(err)')
+				}
+			}
+			else {}
+		}
+		// end catch
+		g.dec_indent()
+		g.writeln('}')
+		// end anon fn
+		g.dec_indent()
+		g.write('})()')
+	}
+	if it.language == .js && ret_sym.name in v_types && ret_sym.name != 'void' {
+		g.write(')')
+	}
+	g.call_stack.delete_last()
+}
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index 90a02b26a3..d35feed7c9 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -406,6 +406,12 @@ pub fn (mut g JsGen) init() {
 		g.definitions.writeln('const \$process = process;')
 	}
 	g.definitions.writeln('function alias(value) { return value; } ')
+
+	g.definitions.writeln('function \$v_fmt(value) { let res = "";
+		if (Object.getPrototypeOf(s).hasOwnProperty("str") && typeof s.str == "function") res = s.str().str
+		else res = s.toString()
+		return res
+  } ')
 }
 
 pub fn (g JsGen) hashes() string {
@@ -1323,11 +1329,14 @@ enum FnGenType {
 	function
 	struct_method
 	alias_method
+	iface_method
 }
 
 fn (g &JsGen) fn_gen_type(it &ast.FnDecl) FnGenType {
 	if it.is_method && g.table.get_type_symbol(it.params[0].typ).kind == .alias {
 		return .alias_method
+	} else if it.is_method && g.table.get_type_symbol(it.params[0].typ).kind == .interface_ {
+		return .iface_method
 	} else if it.is_method || it.no_body {
 		return .struct_method
 	} else {
@@ -1366,7 +1375,7 @@ fn (mut g JsGen) gen_method_decl(it ast.FnDecl, typ FnGenType) {
 	unsafe {
 		g.fn_decl = &it
 	}
-	if typ == .alias_method {
+	if typ == .alias_method || typ == .iface_method {
 		sym := g.table.get_final_type_symbol(it.params[0].typ.set_nr_muls(0))
 		name := g.js_name(sym.name)
 		if name in js.v_types {
@@ -1443,13 +1452,17 @@ fn (mut g JsGen) gen_method_decl(it ast.FnDecl, typ FnGenType) {
 	}
 
 	g.stmts(it.stmts)
-	g.write('}')
+	g.writeln('}')
+
 	if is_main {
 		g.write(')();')
+	} else if typ != .struct_method {
+		// g.write(';')
 	}
-	if typ == .struct_method || typ == .alias_method {
+	if typ == .struct_method || typ == .alias_method || typ == .iface_method {
 		g.writeln('\n')
 	}
+
 	g.fn_decl = voidptr(0)
 }
 
@@ -1620,7 +1633,7 @@ fn (mut g JsGen) gen_interface_decl(it ast.InterfaceDecl) {
 	// This is a hack to make the interface's type accessible outside its namespace
 	// TODO: interfaces are always `pub`?
 	name := g.js_name(it.name)
-	g.push_pub_var('/** @type $name */\n\t\t$name: undefined')
+	g.push_pub_var('/** @type $name */\n\t\t$name')
 	g.writeln('function ${g.js_name(it.name)} (arg) { return arg; }')
 }
 
@@ -1828,217 +1841,6 @@ fn (mut g JsGen) gen_array_init_values(exprs []ast.Expr) {
 	g.write(']')
 }
 
-fn (mut g JsGen) gen_method_call(it ast.CallExpr) bool {
-	g.call_stack << it
-
-	mut name := g.js_name(it.name)
-	call_return_is_optional := it.return_type.has_flag(.optional)
-	if call_return_is_optional {
-		g.writeln('(function(){')
-		g.inc_indent()
-		g.writeln('try {')
-		g.inc_indent()
-		g.write('return builtin.unwrap(')
-	}
-	sym := g.table.get_type_symbol(it.receiver_type)
-	if sym.kind == .array {
-		if sym.kind == .array && it.name in ['map', 'filter'] {
-			g.expr(it.left)
-			mut ltyp := it.left_type
-			for ltyp.is_ptr() {
-				g.write('.val')
-				ltyp = ltyp.deref()
-			}
-			g.write('.')
-			// Prevent 'it' from getting shadowed inside the match
-			node := it
-			g.write(it.name)
-			g.write('(')
-			expr := node.args[0].expr
-			match expr {
-				ast.AnonFn {
-					g.gen_fn_decl(expr.decl)
-					g.write(')')
-					return true
-				}
-				ast.Ident {
-					if expr.kind == .function {
-						g.write(g.js_name(expr.name))
-						g.write(')')
-						return true
-					} else if expr.kind == .variable {
-						v_sym := g.table.get_type_symbol(expr.var_info().typ)
-						if v_sym.kind == .function {
-							g.write(g.js_name(expr.name))
-							g.write(')')
-							return true
-						}
-					}
-				}
-				else {}
-			}
-
-			g.write('it => ')
-			g.expr(node.args[0].expr)
-			g.write(')')
-			return true
-		}
-
-		left_sym := g.table.get_type_symbol(it.left_type)
-		if left_sym.kind == .array {
-			if it.name in special_array_methods {
-				g.expr(it.left)
-				mut ltyp := it.left_type
-				for ltyp.is_ptr() {
-					g.write('.val')
-					ltyp = ltyp.deref()
-				}
-				g.write('.')
-
-				g.gen_array_method_call(it)
-				return true
-			}
-		}
-	}
-
-	// interfaces require dynamic dispatch. To obtain method table we use getPrototypeOf
-	g.write('Object.getPrototypeOf(')
-	g.expr(it.left)
-	mut ltyp := it.left_type
-	for ltyp.is_ptr() {
-		g.write('.val')
-		ltyp = ltyp.deref()
-	}
-	g.write(').$name .call(')
-	g.expr(it.left)
-	g.write(',')
-	for i, arg in it.args {
-		g.expr(arg.expr)
-		if i != it.args.len - 1 {
-			g.write(', ')
-		}
-	}
-	// end method call
-	g.write(')')
-
-	if call_return_is_optional {
-		// end unwrap
-		g.writeln(')')
-		g.dec_indent()
-		// begin catch block
-		g.writeln('} catch(err) {')
-		g.inc_indent()
-		// gen or block contents
-		match it.or_block.kind {
-			.block {
-				if it.or_block.stmts.len > 1 {
-					g.stmts(it.or_block.stmts[..it.or_block.stmts.len - 1])
-				}
-				// g.write('return ')
-				g.stmt(it.or_block.stmts.last())
-			}
-			.propagate {
-				panicstr := '`optional not set (\${err})`'
-				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
-					g.writeln('return builtin.panic($panicstr)')
-				} else {
-					g.writeln('builtin.js_throw(err)')
-				}
-			}
-			else {}
-		}
-		// end catch
-		g.dec_indent()
-		g.writeln('}')
-		// end anon fn
-		g.dec_indent()
-		g.write('})()')
-	}
-	g.call_stack.delete_last()
-	return true
-}
-
-fn (mut g JsGen) gen_call_expr(it ast.CallExpr) {
-	if it.is_method {
-		if g.gen_method_call(it) {
-			return
-		}
-	}
-	g.call_stack << it
-	mut name := g.js_name(it.name)
-	ret_sym := g.table.get_type_symbol(it.return_type)
-	if it.language == .js && ret_sym.name in js.v_types && ret_sym.name != 'void' {
-		g.write('new ')
-		if g.ns.name != 'builtin' {
-			g.write('builtin.')
-		}
-		g.write(ret_sym.name)
-		g.write('(')
-	}
-	call_return_is_optional := it.return_type.has_flag(.optional)
-	if call_return_is_optional {
-		g.writeln('(function(){')
-		g.inc_indent()
-		g.writeln('try {')
-		g.inc_indent()
-		g.write('return builtin.unwrap(')
-	}
-
-	g.expr(it.left)
-
-	if name in g.builtin_fns {
-		g.write('builtin.')
-	}
-
-	g.write('${name}(')
-	for i, arg in it.args {
-		g.expr(arg.expr)
-		if i != it.args.len - 1 {
-			g.write(', ')
-		}
-	}
-	// end method call
-	g.write(')')
-	if call_return_is_optional {
-		// end unwrap
-		g.writeln(')')
-		g.dec_indent()
-		// begin catch block
-		g.writeln('} catch(err) {')
-		g.inc_indent()
-		// gen or block contents
-		match it.or_block.kind {
-			.block {
-				if it.or_block.stmts.len > 1 {
-					g.stmts(it.or_block.stmts[..it.or_block.stmts.len - 1])
-				}
-
-				//	g.write('return ')
-				g.stmt(it.or_block.stmts.last())
-			}
-			.propagate {
-				panicstr := '`optional not set (\${err})`'
-				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
-					g.writeln('return builtin.panic($panicstr)')
-				} else {
-					g.writeln('builtin.js_throw(err)')
-				}
-			}
-			else {}
-		}
-		// end catch
-		g.dec_indent()
-		g.writeln('}')
-		// end anon fn
-		g.dec_indent()
-		g.write('})()')
-	}
-	if it.language == .js && ret_sym.name in js.v_types && ret_sym.name != 'void' {
-		g.write(')')
-	}
-	g.call_stack.delete_last()
-}
-
 fn (mut g JsGen) gen_ident(node ast.Ident) {
 	mut name := g.js_name(node.name)
 	if node.kind == .blank_ident || name in ['', '_'] {
@@ -2337,8 +2139,17 @@ fn (mut g JsGen) match_expr_sumtype(node ast.MatchExpr, is_expr bool, cond_var M
 				if sym.kind == .sum_type {
 					g.write(' instanceof ')
 					g.expr(branch.exprs[sumtype_index])
-				} else {
-					panic('TODO: Generate match for interfaces')
+				} else if sym.kind == .interface_ {
+					if branch.exprs[sumtype_index] is ast.TypeNode {
+						g.write(' instanceof ')
+						g.expr(branch.exprs[sumtype_index])
+					} else {
+						g.write(' instanceof ')
+						if g.ns.name != 'builtin' {
+							g.write('builtin.')
+						}
+						g.write('None__')
+					}
 				}
 				if is_expr && tmp_var.len == 0 {
 					g.write(') ? ')
diff --git a/vlib/v/gen/js/str.v b/vlib/v/gen/js/str.v
new file mode 100644
index 0000000000..ba963b17e8
--- /dev/null
+++ b/vlib/v/gen/js/str.v
@@ -0,0 +1,85 @@
+module js
+
+import v.ast
+
+fn (mut g JsGen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
+	mut typ := etype
+	if etype.has_flag(.shared_f) {
+		typ = typ.clear_flag(.shared_f).set_nr_muls(0)
+	}
+
+	mut sym := g.table.get_type_symbol(typ)
+
+	if mut sym.info is ast.Alias {
+		parent_sym := g.table.get_type_symbol(sym.info.parent_type)
+		if parent_sym.has_method('str') {
+			typ = sym.info.parent_type
+			sym = parent_sym
+		}
+	}
+
+	sym_has_str_method, str_method_expects_ptr, _ := sym.str_method_info()
+	if typ.has_flag(.variadic) {
+		// todo(playX): generate str method just like in the C backend
+		g.write('new string(')
+		g.expr(expr)
+		g.write('.valueOf()')
+		g.write('.toString())')
+	} else if typ == ast.string_type {
+		g.expr(expr)
+	} else if typ == ast.bool_type {
+		g.write('new string(')
+		g.expr(expr)
+		g.write('.valueOf() ? "true" : "false")')
+	} else if sym.kind == .none_ {
+		g.write('new string("<none>")')
+	} else if sym.kind == .enum_ {
+		g.write('new string(')
+		if expr !is ast.EnumVal {
+			g.expr(expr)
+			g.write('.valueOf()')
+			g.write('.toString()')
+		} else {
+			g.write('"')
+			g.expr(expr)
+			g.write('"')
+		}
+		g.write(')')
+	} else if sym.kind == .interface_ && sym_has_str_method {
+		is_ptr := typ.is_ptr()
+		g.write(sym.mod.replace_once('${g.ns.name}.', ''))
+		g.write('.')
+		g.write(sym.name)
+		g.write('.prototype.str.call(')
+		g.expr(expr)
+		if !str_method_expects_ptr && is_ptr {
+			g.gen_deref_ptr(typ)
+		}
+		g.write(')')
+	}
+	//|| sym.kind in [.array, .array_fixed, .map, .struct_, .multi_return,.sum_type, .interface_]
+	else if sym_has_str_method {
+		g.write('new string(')
+		g.write('Object.getPrototypeOf(/*str exists*/')
+		g.expr(expr)
+		is_ptr := typ.is_ptr()
+		g.gen_deref_ptr(typ)
+		g.write(').str.call(')
+		g.expr(expr)
+		if !str_method_expects_ptr && is_ptr {
+			g.gen_deref_ptr(typ)
+		}
+
+		g.write('))')
+	} else if sym.kind == .struct_ && !sym_has_str_method {
+		g.write('new string(')
+		g.expr(expr)
+		g.gen_deref_ptr(typ)
+		g.write('.toString())')
+	} else {
+		g.write('new string(')
+		g.expr(expr)
+		g.gen_deref_ptr(typ)
+		g.write('.valueOf().toString())')
+	}
+}