jsgen: fix array initialization with "index" and "it" (fix #24397) (#24429)

Author: gchumillas

vlib/v/gen/js/js.v

@@ -2052,8 +2052,8 @@ fn (mut g JsGen) gen_array_init_expr(it ast.ArrayInit) {
 		g.writeln('(function(length) {')
 		g.inc_indent()
 		g.writeln('const ${t1} = [];')
-		g.write('for (let it = 0; it < length')
-		g.writeln('; it++) {')
+		g.write('for (let it = 0, index = 0; index < length')
+		g.writeln('; it++, index++) {')
 		g.inc_indent()
 		g.write('${t1}.push(')
 		if it.has_init {

vlib/v/gen/js/tests/array.v

@@ -20,6 +20,17 @@ fn vararg_test() {
 fn main() {
 	vararg_test()
 
+	// index initializations
+	list1 := []string{len: 3, init: 'Item ${index}'}
+	list2 := []string{len: 3, init: 'Item ${it}'}
+	list3 := []int{len: 3, init: index}
+	list4 := []string{len: 4, init: '${index}:${it * 2}'}
+	println(list1)
+	println(list2)
+	println(list1 == list2)
+	println(list3)
+	println(list4)
+
 	arr1 := ['Hello', 'JS', 'Backend']
 	mut arr2 := [1, 2, 3, 4, 5]