State and Decorate#

You can extend Elysia to fit your need. This is useful when you need to access extra values in a handler (e.g. a database connection).

In summary:

• state: assign value to Context.store (a global state object of the Elysia instance)
• decorate: assign value to Context

Example#

app
  .state("version", 1)
  .decorate("getDate", () => Date.now())
  .get("/version", ({ getDate, store: { version } }) => `${version} ${getDate()}`);

• version is registered using state, and accessible via Context.store.version.
• getDate is registered using decorate, and accessible via Context.getDate.

Remap#

By providing a function as a first parameters, the callback will accept current value, allowing us to remap the value to anything we like.

app
    .state({
        a: "a",
        b: "b"
    })
    // Exclude b state
    .state(({ b, ...rest }) => rest)
    .get('/version', ({
        store: { a }
    }) => a

TypeScript#

You can type state and decorator explicitly using TypeScript with as:

app
    // Will type version as `number | null`
    .state('version', 1 as number | null)
    .get('/version', ({
        store: { version }
    }) => version

If the explicit type doesn't type null or undefined, make sure to set strict to true in tsconfig.json:

// tsconfig.json
{
  "compilerOptions": {
    "strict": true
  }
}