xhr: fix json response

src/xhr/xhr.zig

@@ -57,6 +57,8 @@ pub const XMLHttpRequest = struct {
     };
 
     // TODO use std.json.Value instead, but it causes comptime error.
+    // blocked by https://github.com/lightpanda-io/jsruntime-lib/issues/204
+    // const JSONValue = std.json.Value;
     const JSONValue = u8;
 
     const Response = union(ResponseType) {
@@ -511,6 +513,7 @@ pub const XMLHttpRequest = struct {
             // TODO Let jsonObject be the result of running parse JSON from bytes
             // on this’s received bytes. If that threw an exception, then return
             // null.
+            self.setResponseObjJSON();
         }
 
         if (self.response_obj) |obj| {
@@ -558,7 +561,13 @@ pub const XMLHttpRequest = struct {
 
     // setResponseObjJSON parses the received bytes as a std.json.Value.
     fn setResponseObjJSON(self: *XMLHttpRequest) void {
-        const p = std.json.parseFromSlice(JSONValue, self.alloc, self.response_bytes, .{}) catch {
+        const p = std.json.parseFromSliceLeaky(
+            JSONValue,
+            self.alloc,
+            self.response_bytes.?,
+            .{},
+        ) catch |e| {
+            log.err("parse JSON: {}\n{s}", .{ e, self.response_bytes.? });
             self.response_obj = .{ .Failure = true };
             return;
         };
@@ -652,4 +661,19 @@ pub fn testExecFn(
         .{ .src = "req.response", .ex = "" },
     };
     try checkCases(js_env, &send);
+
+    var json = [_]Case{
+        .{ .src = "const req2 = new XMLHttpRequest()", .ex = "undefined" },
+        .{ .src = "req2.open('GET', 'http://httpbin.io/json')", .ex = "undefined" },
+        .{ .src = "req2.responseType = 'json'", .ex = "json" },
+
+        .{ .src = "req2.send()", .ex = "undefined" },
+
+        // Each case executed waits for all loop callaback calls.
+        // So the url has been retrieved.
+        .{ .src = "req2.status", .ex = "200" },
+        .{ .src = "req2.statusText", .ex = "OK" },
+        .{ .src = "req2.response", .ex = "" },
+    };
+    try checkCases(js_env, &json);
 }