Express-fp NPM

express-fp

Type safe request handlers for Express. TypeScript compatible.

Validate Express requests (body and query objects) using io-ts.
Construct Express responses without mutation using express-result-types.

Example

Below is small example that demonstrates request body and query validation using io-ts and fully typed response construction using express-result-types.

See the full example.

const Body = t.interface({
    name: t.string,
});

const Query = t.interface({
    age: NumberFromString,
});

const requestHandler = wrap(req => {
    const jsonBody = req.body.asJson();

    const maybeQuery = Query.decode({
        age: req.query.get('age').toNullable(),
    }).mapLeft(formatValidationErrors('query'));

    const maybeBody = jsonBody.chain(jsValue =>
        jsValue.validate(Body).mapLeft(formatValidationErrors('body')),
    );

    return maybeQuery
        .chain(query => maybeBody.map(body => ({ query, body })))
        .map(({ query, body }) =>
            Ok.apply(
                new JsValue({
                    // We defined the shape of the request body and the request query parameter
                    // 'age' for validation purposes, but it also gives us static types! For
                    // example, here the type checker knows the types:
                    // - `body.name` is type `string`
                    // - `age` is type `number`
                    name: body.name,
                    age: query.age,
                }),
                jsValueWriteable,
            ),
        )
        .getOrElseL(error => BadRequest.apply(new JsValue(error), jsValueWriteable));
});

app.post('/', requestHandler);

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": "bob" }' "localhost:8080/" | jq '.'
// "Validation errors for query: Expecting NumberFromString at age but instead got: null."

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": "bob" }' "localhost:8080/?age=foo" | jq '.'
// "Validation errors for query: Expecting NumberFromString at age but instead got: \"foo\"."

// ❯ curl --request POST --silent --header 'Content-Type: invalid' \
//     --data '{ "name": "bob" }' "localhost:8080/?age=5" | jq '.'
// "Expecting request header 'Content-Type' to equal 'application/json', but instead got 'invalid'."

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data 'invalid' "localhost:8080/?age=5" | jq '.'
// "JSON parsing error: Unexpected token i in JSON at position 0"

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": 1 }' "localhost:8080/?age=5" | jq '.'
// "Validation errors for body: Expecting string at name but instead got: 1."

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": "bob" }' "localhost:8080/?age=5" | jq '.'
// {
//   "name": "bob",
//   "age": 5
// }