jsgen: fix javascript backend treating u32 as i32 (fix #20499) (#20618)

vlib/v/gen/js/builtin_types.v

@@ -335,7 +335,7 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 	for typ_name in v_types {
 		// TODO: JsDoc
 		match typ_name {
-			'i8', 'i16', 'int', 'u16', 'u32', 'int_literal' {
+			'i8', 'i16', 'int', 'u16', 'int_literal' {
 				// TODO: Bounds checking
 				g.gen_builtin_prototype(
 					typ_name: typ_name
@@ -348,6 +348,19 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 					to_jsval: '+this'
 				)
 			}
+			// u32 requires special handling in JavaScript to correctly represent it as an unsigned 32-bit integer.
+			// The '>>> 0' bit operation ensures it is treated as unsigned, covering the full 0 to 2^32-1 range.
+			'u32' {
+				g.gen_builtin_prototype(
+					typ_name: typ_name
+					default_value: 'new Number(0)'
+					constructor: 'this.val = Math.floor(Number(val) & 0xffffffff) >>> 0'
+					value_of: 'Number(this.val)'
+					to_string: 'this.valueOf().toString()'
+					eq: 'new bool(self.valueOf() === other.valueOf())'
+					to_jsval: '+this'
+				)
+			}
 			// u64 and i64 are so big that their values do not fit into JS number so we use BigInt.
 			'u64' {
 				if g.pref.output_es5 {

vlib/v/gen/js/tests/testdata/u32.out

@@ -0,0 +1,4 @@
+4294967295
+0
+true
+25600000

vlib/v/gen/js/tests/testdata/u32.v

@@ -0,0 +1,7 @@
+fn main() {
+	println(u32(0xFFFFFFFF))
+	println(u32(4294967295) + 1)
+
+	println(u32(42) == u32(42))
+	println(u32(100000) * 256)
+}