Disclaimer: These are just my personal notes to help me articulate concepts I’m learning. They’re not meant to be used as a tutorial.

Why use a custom date scalar type in GraphQL?

Well first, what is a scalar?

A scalar is a type. GraphQL has four default scalar types:

• Int

• Float

• String

• Boolean

Notice there is no Date type.

By default, GraphQL uses seconds internally. This means that even if your database stores a createdAt date in a readable format like 019-06-12 09:49:55.058+06:30, GraphQL will still convert it to a long seconds string like 1560310894541 before returning it to the client, which isn’t very readable.

Also, think about the semantics of this. Imagine you have a schema for a Post type where one of the fields is createdAt. For example:

What should we return for the createdAt field? There is no Date format. So the best we can do is return a string. But this means that the client will receive a non-human readable string of seconds for the createdAt field.

Luckily GraphQL lets us add our own custom scalar types.

We can use a package called graphql-iso-date.

1. Add a Date scalar in your root schema

2. Add a resolver at the highest level of the resolver map that tells the program to return a GraphQLDateTime for the type Date. In my case, I’m doing something like this:

3. Then, in your schema, you can return an actual Date scalar type for the createdAt field on the Post

Now, when we run the post query, we get back a more readable date format: