Error - The type you provided for 'FeedMessageData' is not a valid JSON value

Why this error occurred

You have provided a custom FeedMessageData type for your application, but the type you provided isn’t a (completely) valid JSON value. Values like Date, Map, Set, functions, classes, or unknown aren’t valid JSON.

declare global {  interface Liveblocks {    FeedMessageData: {      // Your own fields go here…      userId: string;      content: string;      status: "streaming" | "complete";      sentAt: Date; // ❌ The issue is here    };  }}

In the example above, the problem is in the sentAt field, because a Date isn’t a valid JSON value.

How to fix it

You’ll need to figure out what part of your provided FeedMessageData type definition isn’t valid JSON. Sometimes this is immediately obvious, like in the example above.

Sometimes the issue may be a bit less obvious:

import type { Json } from "@liveblocks/client";
declare global {  interface Liveblocks {    FeedMessageData: {      content: unknown; // ❌ Unknowns could contain non-JSON      content: Json; // ✅ Prefer using Json    };  }}

By using Json, you can still work with unknown or unspecified values, but still ensure they will be valid JSON.

If you cannot find the root cause

Sometimes types can be complex and the root cause is still unclear. In those cases, there is a small trick you can use. Try to assign your type to the required base type, with this line:

import type { Json } from "@liveblocks/client";
declare global {  interface Liveblocks {    FeedMessageData: MyFeedMessageData;  }}
// Quick debugging snippet to find root causeconst xxx: Json = {} as MyFeedMessageData;//    ^?//    The error will appear here

Now TypeScript will explain why it thinks your type isn’t valid JSON:

Type 'MyFeedMessageData' is not assignable to type 'Json'.  Type 'MyFeedMessageData' is not assignable to type 'JsonObject'.    Property 'sentAt' is incompatible with index signature.      Type 'Date' is not assignable to type 'Json | undefined'.        Type 'Date' is not assignable to type 'JsonObject'.          Index signature for type 'string' is missing in type 'Date'.