jsgen: fix string.runes method (fix #20500) (#24609)

Author: gchumillas

vlib/builtin/js/string.js.v

@@ -7,13 +7,10 @@ pub:
 }
 
 pub fn (s string) runes() []rune {
-	mut runes := []rune{}
-	for i := 0; i < s.len; i++ {
-		mut r := rune(`0`)
-		#r = new rune(s.str[i.val].charCodeAt())
-		runes << r
-	}
-	return runes
+	ret := JS.makeEmptyArray()
+	#for (r of s.str) array_push(ret,new rune(r),false);
+
+	return ret
 }
 
 pub fn (s string) slice(a int, b int) string {

vlib/v/gen/js/tests/string.v

@@ -0,0 +1,66 @@
+fn test_runes() {
+	// Test basic ASCII + emoji
+	r1 := 'hello🎅'.runes()
+	assert r1.len == 6
+	assert r1[0] == `h`
+	assert r1[1] == `e`
+	assert r1[2] == `l`
+	assert r1[3] == `l`
+	assert r1[4] == `o`
+	assert r1[5] == `🎅`
+
+	// Test empty string
+	r2 := ''.runes()
+	assert r2.len == 0
+
+	// Test single character
+	r3 := 'A'.runes()
+	assert r3.len == 1
+	assert r3[0] == `A`
+
+	// Test Unicode characters
+	r4 := 'café'.runes()
+	assert r4.len == 4
+	assert r4[0] == `c`
+	assert r4[1] == `a`
+	assert r4[2] == `f`
+	assert r4[3] == `é`
+
+	// Test multiple emojis
+	r5 := '🎅🎄🎁'.runes()
+	assert r5.len == 3
+	assert r5[0] == `🎅`
+	assert r5[1] == `🎄`
+	assert r5[2] == `🎁`
+
+	// Test mixed ASCII, Unicode and emojis
+	r6 := 'hello世界🌍'.runes()
+	assert r6.len == 8
+	assert r6[0] == `h`
+	assert r6[1] == `e`
+	assert r6[2] == `l`
+	assert r6[3] == `l`
+	assert r6[4] == `o`
+	assert r6[5] == `世`
+	assert r6[6] == `界`
+	assert r6[7] == `🌍`
+
+	// Test special characters
+	r7 := '\n\t'.runes()
+	assert r7.len == 2
+	assert r7[0] == `\n`
+	assert r7[1] == `\t`
+
+	// Test mathematical symbols
+	r8 := 'α+β=γ'.runes()
+	assert r8.len == 5
+	assert r8[0] == `α`
+	assert r8[1] == `+`
+	assert r8[2] == `β`
+	assert r8[3] == `=`
+	assert r8[4] == `γ`
+}
+
+fn main() {
+	test_runes()
+}