js: implement more functions for JS backend (#12167)

vlib/builtin/js/builtin.js.v

@@ -2,8 +2,11 @@ module builtin
 
 // used to generate JS throw statements.
 
+[noreturn]
 pub fn js_throw(s any) {
 	#throw s
+
+	for {}
 }
 
 #let globalPrint;
@@ -46,6 +49,7 @@ pub fn eprint(s string) {
 // Exits the process in node, and halts execution in the browser
 // because `process.exit` is undefined. Workaround for not having
 // a 'real' way to exit in the browser.
+[noreturn]
 pub fn exit(c int) {
 	JS.process.exit(c)
 	js_throw('exit($c)')

vlib/builtin/js/byte.js.v

@@ -68,3 +68,29 @@ pub fn (c byte) is_letter() bool {
 pub fn (c byte) is_alnum() bool {
 	return c.is_letter() || c.is_digit()
 }
+
+// Define this on byte as well, so that we can do `s[0].is_capital()`
+pub fn (c byte) is_capital() bool {
+	return c >= `A` && c <= `Z`
+}
+
+// str_escaped returns the contents of `byte` as an escaped `string`.
+// Example: assert byte(0).str_escaped() == r'`\0`'
+
+pub fn (b byte) str_escaped() string {
+	mut str := ''
+	match b {
+		0 { str = r'`\0`' }
+		7 { str = r'`\a`' }
+		8 { str = r'`\b`' }
+		9 { str = r'`\t`' }
+		10 { str = r'`\n`' }
+		11 { str = r'`\v`' }
+		12 { str = r'`\f`' }
+		13 { str = r'`\r`' }
+		27 { str = r'`\e`' }
+		32...126 { str = b.ascii_str() }
+		else { str = '0x' + b.hex() }
+	}
+	return str
+}

vlib/builtin/js/string.js.v

@@ -900,3 +900,13 @@ pub fn (s []string) join(sep string) string {
 
 // There's no better way to find length of JS String in bytes.
 #Object.defineProperty(string.prototype,"len", { get: function() {return new int(new TextEncoder().encode(this.str).length);}, set: function(l) {/* ignore */ } });
+// index returns the position of the first character of the input string.
+// It will return `none` if the input string can't be found.
+pub fn (s string) index(search string) ?int {
+	res := 0
+	#res.val = s.str.indexOf(search)
+	if res == -1 {
+		return none
+	}
+	return res
+}