diff --git a/vlib/json/json_primitives.v b/vlib/json/json_primitives.v
index f8868b67e1..68c1f9b8f0 100644
--- a/vlib/json/json_primitives.v
+++ b/vlib/json/json_primitives.v
@@ -71,6 +71,11 @@ fn decode_i64(root &C.cJSON) i64 {
 	return i64(root.valuedouble) // i64 is double in C
 }
 
+// TODO: remove when `byte` is removed
+fn decode_byte(root &C.cJSON) byte {
+	return byte(decode_u8(root))
+}
+
 fn decode_u8(root &C.cJSON) u8 {
 	if isnil(root) {
 		return u8(0)
@@ -132,8 +137,6 @@ fn decode_string(root &C.cJSON) string {
 	if isnil(root.valuestring) {
 		return ''
 	}
-	// println('decode string valuestring="$root.valuestring"')
-	// return tos(root.valuestring, _strlen(root.valuestring))
 	return unsafe { tos_clone(&u8(root.valuestring)) } // , _strlen(root.valuestring))
 }
 
@@ -145,6 +148,7 @@ fn decode_bool(root &C.cJSON) bool {
 }
 
 // ///////////////////
+
 fn encode_int(val int) &C.cJSON {
 	return C.cJSON_CreateNumber(val)
 }
@@ -161,6 +165,11 @@ fn encode_i64(val i64) &C.cJSON {
 	return C.cJSON_CreateNumber(val)
 }
 
+// TODO: remove when `byte` is removed
+fn encode_byte(root byte) &C.cJSON {
+	return encode_u8(u8(root))
+}
+
 fn encode_u8(val u8) &C.cJSON {
 	return C.cJSON_CreateNumber(val)
 }
diff --git a/vlib/json/json_test.v b/vlib/json/json_test.v
index 2cb15870b1..dd72c0c469 100644
--- a/vlib/json/json_test.v
+++ b/vlib/json/json_test.v
@@ -27,6 +27,25 @@ fn test_simple() ? {
 	assert y.title == .worker
 }
 
+const currency_id = 'cconst'
+
+struct Price {
+	net         f64
+	currency_id string [json: currencyId] = currency_id
+}
+
+fn test_field_with_default_expr() ? {
+	data := '[{"net":1},{"net":2,"currencyId":"cjson"}]'
+	prices := json.decode([]Price, data)?
+	assert prices == [Price{
+		net: 1
+		currency_id: 'cconst'
+	}, Price{
+		net: 2
+		currency_id: 'cjson'
+	}]
+}
+
 fn test_decode_top_level_array() {
 	s := '[{"name":"Peter", "age": 29}, {"name":"Bob", "age":31}]'
 	x := json.decode([]Employee, s) or { panic(err) }
@@ -454,3 +473,11 @@ fn test_encode_sumtype_defined_ahead() {
 	println(ret)
 	assert ret == '{"value":0,"_type":"GPScale"}'
 }
+
+struct StByteArray {
+	ba []byte
+}
+
+fn test_byte_array() {
+	assert json.encode(StByteArray{ ba: [byte(1), 2, 3, 4, 5] }) == '{"ba":[1,2,3,4,5]}'
+}
diff --git a/vlib/v/ast/types.v b/vlib/v/ast/types.v
index 428e4a67fa..e2c29d2b80 100644
--- a/vlib/v/ast/types.v
+++ b/vlib/v/ast/types.v
@@ -79,7 +79,6 @@ pub fn pref_arch_to_table_language(pref_arch pref.Arch) Language {
 // * Table.type_kind(typ) not TypeSymbol.kind.
 // Each TypeSymbol is entered into `Table.types`.
 // See also: Table.sym.
-
 [minify]
 pub struct TypeSymbol {
 pub:
diff --git a/vlib/v/gen/c/json.v b/vlib/v/gen/c/json.v
index 80aace3dc8..7e7c1e8fd3 100644
--- a/vlib/v/gen/c/json.v
+++ b/vlib/v/gen/c/json.v
@@ -7,16 +7,21 @@ import v.ast
 import v.util
 import strings
 
-// TODO replace with comptime code generation.
-// TODO remove cJSON dependency.
-// OLD: User decode_User(string js) {
-// now it's
+// TODO: replace with comptime code generation.
+// TODO: remove cJSON dependency.
+
+// Old:
+// `User decode_User(string js) {`
+// now it's:
+// ```
 // User decode_User(cJSON* root) {
-// User res;
-// res.name = decode_string(js_get(root, "name"));
-// res.profile = decode_Profile(js_get(root, "profile"));
-// return res;
+//     User res;
+//     res.name = decode_string(js_get(root, "name"));
+//     res.profile = decode_Profile(js_get(root, "profile"));
+//     return res;
 // }
+// ```
+
 // Codegen json_decode/encode funcs
 fn (mut g Gen) gen_json_for_type(typ ast.Type) {
 	utyp := g.unwrap_generic(typ).set_nr_muls(0)
@@ -40,10 +45,9 @@ fn (mut g Gen) gen_jsons() {
 		sym := g.table.sym(utyp)
 		styp := g.typ(utyp)
 		g.register_optional(utyp)
-		// println('gen_json_for_type($sym.name)')
 		// decode_TYPE funcs receive an actual cJSON* object to decode
 		// cJSON_Parse(str) call is added by the compiler
-		// Code gen decoder
+		// Codegen decoder
 		dec_fn_name := js_dec_name(styp)
 		dec_fn_dec := '${option_name}_$styp ${dec_fn_name}(cJSON* root)'
 
@@ -101,7 +105,7 @@ $dec_fn_dec {
 	}
 ')
 		g.json_forward_decls.writeln('$dec_fn_dec;')
-		// Code gen encoder
+		// Codegen encoder
 		// encode_TYPE funcs receive an object to encode
 		enc_fn_name := js_enc_name(styp)
 		enc_fn_dec := 'cJSON* ${enc_fn_name}($styp val)'
@@ -116,7 +120,6 @@ $enc_fn_dec {
 			g.gen_json_for_type(value_type)
 			dec.writeln(g.decode_array(value_type))
 			enc.writeln(g.encode_array(value_type))
-			// enc += g.encode_array(t)
 		} else if sym.kind == .map {
 			// Handle maps
 			m := sym.info as ast.Map
@@ -156,7 +159,6 @@ $enc_fn_dec {
 			g.gen_struct_enc_dec(sym.info, styp, mut enc, mut dec)
 		}
 		// cJSON_delete
-		// p.cgen.fns << '$dec return opt_ok(res); \n}'
 		dec.writeln('\t${option_name}_$styp ret;')
 		dec.writeln('\topt_ok2(&res, ($option_name*)&ret, sizeof(res));')
 		dec.writeln('\treturn ret;\n}')
@@ -396,17 +398,41 @@ fn (mut g Gen) gen_struct_enc_dec(type_info ast.TypeInfo, styp string, mut enc s
 			if is_js_prim(field_type) {
 				tmp := g.new_tmp_var()
 				gen_js_get(styp, tmp, name, mut dec, is_required)
+				if field.has_default_expr {
+					dec.writeln('\tif (jsonroot_$tmp) {')
+				}
 				dec.writeln('\tres.${c_name(field.name)} = $dec_name (jsonroot_$tmp);')
+				if field.has_default_expr {
+					dec.writeln('\t} else {')
+					dec.writeln('\tres.${c_name(field.name)} = ${g.expr_string(field.default_expr)};')
+					dec.writeln('\t}')
+				}
 			} else if field_sym.kind == .enum_ {
 				tmp := g.new_tmp_var()
 				gen_js_get(styp, tmp, name, mut dec, is_required)
+				if field.has_default_expr {
+					dec.writeln('\tif (jsonroot_$tmp) {')
+				}
 				dec.writeln('\tres.${c_name(field.name)} = json__decode_u64(jsonroot_$tmp);')
+				if field.has_default_expr {
+					dec.writeln('\t} else {')
+					dec.writeln('\tres.${c_name(field.name)} = ${g.expr_string(field.default_expr)};')
+					dec.writeln('\t}')
+				}
 			} else if field_sym.name == 'time.Time' {
 				// time struct requires special treatment
 				// it has to be decoded from a unix timestamp number
 				tmp := g.new_tmp_var()
 				gen_js_get(styp, tmp, name, mut dec, is_required)
+				if field.has_default_expr {
+					dec.writeln('\tif (jsonroot_$tmp) {')
+				}
 				dec.writeln('\tres.${c_name(field.name)} = time__unix(json__decode_u64(jsonroot_$tmp));')
+				if field.has_default_expr {
+					dec.writeln('\t} else {')
+					dec.writeln('\tres.${c_name(field.name)} = ${g.expr_string(field.default_expr)};')
+					dec.writeln('\t}')
+				}
 			} else if field_sym.kind == .alias {
 				alias := field_sym.info as ast.Alias
 				parent_type := g.typ(alias.parent_type)
@@ -414,17 +440,41 @@ fn (mut g Gen) gen_struct_enc_dec(type_info ast.TypeInfo, styp string, mut enc s
 				if is_js_prim(parent_type) {
 					tmp := g.new_tmp_var()
 					gen_js_get(styp, tmp, name, mut dec, is_required)
+					if field.has_default_expr {
+						dec.writeln('\tif (jsonroot_$tmp) {')
+					}
 					dec.writeln('\tres.${c_name(field.name)} = $parent_dec_name (jsonroot_$tmp);')
+					if field.has_default_expr {
+						dec.writeln('\t} else {')
+						dec.writeln('\tres.${c_name(field.name)} = ${g.expr_string(field.default_expr)};')
+						dec.writeln('\t}')
+					}
 				} else {
 					g.gen_json_for_type(field.typ)
 					tmp := g.new_tmp_var()
 					gen_js_get_opt(dec_name, field_type, styp, tmp, name, mut dec, is_required)
+					if field.has_default_expr {
+						dec.writeln('\tif (jsonroot_$tmp) {')
+					}
 					dec.writeln('\tres.${c_name(field.name)} = *($field_type*) ${tmp}.data;')
+					if field.has_default_expr {
+						dec.writeln('\t} else {')
+						dec.writeln('\tres.${c_name(field.name)} = ${g.expr_string(field.default_expr)};')
+						dec.writeln('\t}')
+					}
 				}
 			} else {
 				tmp := g.new_tmp_var()
 				gen_js_get_opt(dec_name, field_type, styp, tmp, name, mut dec, is_required)
+				if field.has_default_expr {
+					dec.writeln('\tif (jsonroot_$tmp) {')
+				}
 				dec.writeln('\tres.${c_name(field.name)} = *($field_type*) ${tmp}.data;')
+				if field.has_default_expr {
+					dec.writeln('\t} else {')
+					dec.writeln('\tres.${c_name(field.name)} = ${g.expr_string(field.default_expr)};')
+					dec.writeln('\t}')
+				}
 			}
 		}
 		// Encoding
@@ -453,7 +503,7 @@ fn (mut g Gen) gen_struct_enc_dec(type_info ast.TypeInfo, styp string, mut enc s
 }
 
 fn gen_js_get(styp string, tmp string, name string, mut dec strings.Builder, is_required bool) {
-	dec.writeln('\tcJSON *jsonroot_$tmp = js_get(root,"$name");')
+	dec.writeln('\tcJSON *jsonroot_$tmp = js_get(root, "$name");')
 	if is_required {
 		dec.writeln('\tif(jsonroot_$tmp == 0) {')
 		dec.writeln('\t\treturn (${option_name}_$styp){ .state = 2, .err = _v_error(_SLIT("expected field \'$name\' is missing")), .data = {0} };')
diff --git a/vlib/v/parser/struct.v b/vlib/v/parser/struct.v
index 6502be94f6..c36f59a585 100644
--- a/vlib/v/parser/struct.v
+++ b/vlib/v/parser/struct.v
@@ -40,11 +40,6 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 		return ast.StructDecl{}
 	}
 	mut name := p.check_name()
-	// defer {
-	// if name.contains('App') {
-	// println('end of struct decl $name')
-	// }
-	// }
 	if name.len == 1 && name[0].is_capital() {
 		p.error_with_pos('single letter capital names are reserved for generic template types.',
 			name_pos)
@@ -328,9 +323,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 		p.error_with_pos('invalid recursive struct `$orig_name`', name_pos)
 		return ast.StructDecl{}
 	}
-	mut ret := 0
-	// println('reg type symbol $name mod=$p.mod')
-	ret = p.table.register_sym(t)
+	mut ret := p.table.register_sym(t)
 	// allow duplicate c struct declarations
 	if ret == -1 && language != .c {
 		p.error_with_pos('cannot register struct `$name`, another type with this name exists',