jsgen: fix inconsistent output (u32) in JS backend (#20691)

vlib/v/gen/js/builtin_types.v

@@ -348,15 +348,25 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 					to_jsval: '+this'
 				)
 			}
-			// u16 / u32 requires special handling in JavaScript to correctly represent it as an unsigned 32-bit integer.
+			// u16 and u32 requires special handling in JavaScript to correctly represent it.
-			// The '>>> 0' bit operation ensures it is treated as unsigned, covering the full 0 to 2^32-1 range.
+			// u16, '>>> 0' combined with a mask of 0xffff limits it to the 0 to 2^16-1 range, correctly handling values as unsigned 16-bit integers.
-			// For u16, '>>> 0' combined with a mask of 0xffff limits it to the 0 to 2^16-1 range, correctly handling values as unsigned 16-bit integers.
+			'u16' {
-			'u16', 'u32' {
 				g.gen_builtin_prototype(
 					typ_name: typ_name
 					default_value: 'new Number(0)'
-					constructor: "this.val = Math.floor(Number(val) & ('" + typ_name +
+					constructor: 'this.val = Math.floor(Number(val) & 0xffff) >>> 0'
-						'\' === "u16" ? 0xffff : 0xffffffff)) >>> 0'
+					value_of: 'Number(this.val)'
+					to_string: 'this.valueOf().toString()'
+					eq: 'new bool(self.valueOf() === other.valueOf())'
+					to_jsval: '+this'
+				)
+			}
+			// u32 '>>> 0' combined with a mask of 0xffffffff limits it to the 0 to 2^32-1 range, correctly handling values as unsigned 32-bit integers.
+			'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())'

vlib/v/gen/js/str.v

@@ -120,11 +120,19 @@ fn (mut g JsGen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 		is_var_mut := expr.is_auto_deref_var()
 		str_fn_name := g.get_str_fn(typ)
 		g.write('${str_fn_name}(')
+
 		if str_method_expects_ptr && !is_ptr {
 			g.write('new \$ref(')
 		}
+		if typ == ast.u32_type && expr is ast.CastExpr {
+			g.write('new u32(')
+		}
 
 		g.expr(expr)
+
+		if typ == ast.u32_type && expr is ast.CastExpr {
+			g.write(')')
+		}
 		if (!str_method_expects_ptr && is_ptr && !is_shared) || is_var_mut {
 			g.write('.val')
 		}

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

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