exp/template/html: non-semantics changing tweaks to js{,_test}.go

R=nigeltao
CC=golang-dev
https://golang.org/cl/4962049

src/pkg/exp/template/html/js.go

@@ -179,7 +179,6 @@ func jsStrEscaper(args ...interface{}) string {
 	for i, r := range s {
 		var repl string
 		switch r {
-		// All cases must appear in the IndexAny call above.
 		case 0:
 			repl = `\0`
 		case '\t':
@@ -222,7 +221,7 @@ func jsStrEscaper(args ...interface{}) string {
 		b.WriteString(repl)
 		written = i + utf8.RuneLen(r)
 	}
-	if b.Len() == 0 {
+	if written == 0 {
 		return s
 	}
 	b.WriteString(s[written:])
@@ -247,7 +246,6 @@ func jsRegexpEscaper(args ...interface{}) string {
 	for i, r := range s {
 		var repl string
 		switch r {
-		// All cases must appear in the IndexAny call above.
 		case 0:
 			repl = `\0`
 		case '\t':
@@ -316,7 +314,7 @@ func jsRegexpEscaper(args ...interface{}) string {
 		b.WriteString(repl)
 		written = i + utf8.RuneLen(r)
 	}
-	if b.Len() == 0 {
+	if written == 0 {
 		return s
 	}
 	b.WriteString(s[written:])

src/pkg/exp/template/html/js_test.go

@@ -205,6 +205,10 @@ func TestJSStrEscaper(t *testing.T) {
 		{"+ADw-script+AD4-alert(1)+ADw-/script+AD4-",
 			`\x2bADw-script\x2bAD4-alert(1)\x2bADw-\/script\x2bAD4-`,
 		},
+		// Invalid UTF-8 sequence
+		{"foo\xA0bar", "foo\xA0bar"},
+		// Invalid unicode scalar value.
+		{"foo\xed\xa0\x80bar", "foo\xed\xa0\x80bar"},
 	}
 
 	for _, test := range tests {