diff --git a/compiler/natives/src/time/format.go b/compiler/natives/src/time/format.go
new file mode 100644
index 000000000..0e1594c19
--- /dev/null
+++ b/compiler/natives/src/time/format.go
@@ -0,0 +1,79 @@
+//go:build js
+// +build js
+
+package time
+
+// copied and replaced for go1.20 temporarily without generics.
+func atoi(sAny any) (x int, err error) {
+	s := asBytes(sAny)
+	neg := false
+	if len(s) > 0 && (s[0] == '-' || s[0] == '+') {
+		neg = s[0] == '-'
+		s = s[1:]
+	}
+	q, remStr, err := leadingInt(s)
+	rem := []byte(remStr)
+	x = int(q)
+	if err != nil || len(rem) > 0 {
+		return 0, atoiError
+	}
+	if neg {
+		x = -x
+	}
+	return x, nil
+}
+
+// copied and replaced for go1.20 temporarily without generics.
+func isDigit(sAny any, i int) bool {
+	s := asBytes(sAny)
+	if len(s) <= i {
+		return false
+	}
+	c := s[i]
+	return '0' <= c && c <= '9'
+}
+
+// copied and replaced for go1.20 temporarily without generics.
+func parseNanoseconds(sAny any, nbytes int) (ns int, rangeErrString string, err error) {
+	value := asBytes(sAny)
+	if !commaOrPeriod(value[0]) {
+		err = errBad
+		return
+	}
+	if nbytes > 10 {
+		value = value[:10]
+		nbytes = 10
+	}
+	if ns, err = atoi(value[1:nbytes]); err != nil {
+		return
+	}
+	if ns < 0 {
+		rangeErrString = "fractional second"
+		return
+	}
+	scaleDigits := 10 - nbytes
+	for i := 0; i < scaleDigits; i++ {
+		ns *= 10
+	}
+	return
+}
+
+// copied and replaced for go1.20 temporarily without generics.
+func leadingInt(sAny any) (x uint64, rem string, err error) {
+	s := asBytes(sAny)
+	i := 0
+	for ; i < len(s); i++ {
+		c := s[i]
+		if c < '0' || c > '9' {
+			break
+		}
+		if x > 1<<63/10 {
+			return 0, rem, errLeadingInt
+		}
+		x = x*10 + uint64(c) - '0'
+		if x > 1<<63 {
+			return 0, rem, errLeadingInt
+		}
+	}
+	return x, string(s[i:]), nil
+}
diff --git a/compiler/natives/src/time/format_rfc3339.go b/compiler/natives/src/time/format_rfc3339.go
new file mode 100644
index 000000000..7c69bfc95
--- /dev/null
+++ b/compiler/natives/src/time/format_rfc3339.go
@@ -0,0 +1,85 @@
+//go:build js
+// +build js
+
+package time
+
+import "errors"
+
+// added for go1.20 temporarily without generics.
+func asBytes(s any) []byte {
+	switch t := s.(type) {
+	case []byte:
+		return t
+	case string:
+		return []byte(t)
+	default:
+		panic(errors.New(`unexpected type passed to asBytes, expected string or []bytes`))
+	}
+}
+
+// copied and replaced for go1.20 temporarily without generics.
+func parseRFC3339(sAny any, local *Location) (Time, bool) {
+	s := asBytes(sAny)
+	ok := true
+	parseUint := func(s []byte, min, max int) (x int) {
+		for _, c := range s {
+			if c < '0' || '9' < c {
+				ok = false
+				return min
+			}
+			x = x*10 + int(c) - '0'
+		}
+		if x < min || max < x {
+			ok = false
+			return min
+		}
+		return x
+	}
+
+	if len(s) < len("2006-01-02T15:04:05") {
+		return Time{}, false
+	}
+	year := parseUint(s[0:4], 0, 9999)
+	month := parseUint(s[5:7], 1, 12)
+	day := parseUint(s[8:10], 1, daysIn(Month(month), year))
+	hour := parseUint(s[11:13], 0, 23)
+	min := parseUint(s[14:16], 0, 59)
+	sec := parseUint(s[17:19], 0, 59)
+	if !ok || !(s[4] == '-' && s[7] == '-' && s[10] == 'T' && s[13] == ':' && s[16] == ':') {
+		return Time{}, false
+	}
+	s = s[19:]
+
+	var nsec int
+	if len(s) >= 2 && s[0] == '.' && isDigit(s, 1) {
+		n := 2
+		for ; n < len(s) && isDigit(s, n); n++ {
+		}
+		nsec, _, _ = parseNanoseconds(s, n)
+		s = s[n:]
+	}
+
+	t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
+	if len(s) != 1 || s[0] != 'Z' {
+		if len(s) != len("-07:00") {
+			return Time{}, false
+		}
+		hr := parseUint(s[1:3], 0, 23)
+		mm := parseUint(s[4:6], 0, 59)
+		if !ok || !((s[0] == '-' || s[0] == '+') && s[3] == ':') {
+			return Time{}, false
+		}
+		zoneOffset := (hr*60 + mm) * 60
+		if s[0] == '-' {
+			zoneOffset *= -1
+		}
+		t.addSec(-int64(zoneOffset))
+
+		if _, offset, _, _, _ := local.lookup(t.unixSec()); offset == zoneOffset {
+			t.setLoc(local)
+		} else {
+			t.setLoc(FixedZone("", zoneOffset))
+		}
+	}
+	return t, true
+}