strconv,v.gen.js: proper optionals returns, strconv compiles to the JS backend (#11364)

vlib/strconv/number_to_base.c.v

@@ -0,0 +1,61 @@
+module strconv
+
+const base_digits = '0123456789abcdefghijklmnopqrstuvwxyz'
+
+// format_int returns the string representation of the number n in base `radix`
+// for digit values > 10, this function uses the small latin leters a-z.
+[manualfree]
+pub fn format_int(n i64, radix int) string {
+	unsafe {
+		if radix < 2 || radix > 36 {
+			panic('invalid radix: $radix . It should be => 2 and <= 36')
+		}
+		if n == 0 {
+			return '0'
+		}
+		mut n_copy := n
+		mut sign := ''
+		if n < 0 {
+			sign = '-'
+			n_copy = -n_copy
+		}
+		mut res := ''
+		for n_copy != 0 {
+			tmp_0 := res
+			tmp_1 := strconv.base_digits[n_copy % radix].ascii_str()
+			res = tmp_1 + res
+			tmp_0.free()
+			tmp_1.free()
+			// res = base_digits[n_copy % radix].ascii_str() + res
+			n_copy /= radix
+		}
+		return '$sign$res'
+	}
+}
+
+// format_uint returns the string representation of the number n in base `radix`
+// for digit values > 10, this function uses the small latin leters a-z.
+[manualfree]
+pub fn format_uint(n u64, radix int) string {
+	unsafe {
+		if radix < 2 || radix > 36 {
+			panic('invalid radix: $radix . It should be => 2 and <= 36')
+		}
+		if n == 0 {
+			return '0'
+		}
+		mut n_copy := n
+		mut res := ''
+		uradix := u64(radix)
+		for n_copy != 0 {
+			tmp_0 := res
+			tmp_1 := strconv.base_digits[n_copy % uradix].ascii_str()
+			res = tmp_1 + res
+			tmp_0.free()
+			tmp_1.free()
+			// res = base_digits[n_copy % uradix].ascii_str() + res
+			n_copy /= uradix
+		}
+		return res
+	}
+}