ajaxian

Ajaxian is a small wrapper around the XMLHttpRequest object. It borrows heavily from the Elm Http module. In many ways it's not all that different from other http libraries: build a request, send it to the server, and then handle the response. The emphasis here is on handling error responses correctly and consistently, without resorting to thrown exceptions.

Because it uses XMLHttpRequest, Ajaxian can only be used from the browser (or a browser-like environment, like Electron). Browserify, Webpack, or some similar tool may be required when packaging for deploy.

tasks

Instead of Promises, Ajaxian uses Futures (here called Tasks, from the Taskarian library). Tasks are lazy and will not execute until forked. This means a Task can be returned from a pure function. Tasks are also composable. You can build a complex chain of behaviors, while strictly controlling exactly when the side effects happen. In this way I prefer them over Promises, which are stateful and initiate side effects as soon as they are instantiated.

errors

Ajaxian does not throw errors for failed requests. Instead, failed requests are returned as one of several different types of errors. Error conditions are documented this way because I believe that you create a better user experience when you handle error conditions gracefully. I want to provide the tools for doing that.

All of the error types are documented in the HttpError module.

decoders

Decoders are another idea stolen from Elm. A decoder is a function that converts the response body of a request into a data structure that can be used by the application.

Ajaxian expects the decoder to return the results wrapped in a Result object. If the data passes muster, then the decoder should return the data wrapped in an Ok object. If the data is incorrect, then an error message wrapped will be wrapped in an Err object. This will result in a BadPayload error.

If you are building a json heavy application, I would recommend checking out jsonous. This library is specifically built for creating composable decoders for handling json content.

installing

npm install --save ajaxian

yarn add ajaxian

usage

import { toHttpTask, Request, header } from 'ajaxian';
import { ok } from 'resulty';

// Create a request object. This is a TS example.
const request: Request<{}> = {
  url: '/some_end_point',
  method: 'post',
  data: { foo: 'bar' },
  timeout: 0,
  headers: [header('X-Some-Header', 'baz')],
  withCredentials: true,
  decoder: () => ok({}),
};

toHttpTask(request).fork(
  err => console.error(err),
  data => console.log("Success!", data)
);

There are some convenience builders for making requests, too:

import { post } from 'ajaxian';

const request = post('/some_end_point', { foo: bar }, () => ok({}))
  .withHeader(header('X-Some-Header', 'baz'));

It is also possible to abort an HTTP request before it completes. Forking the HTTP task returns an abort function from the underlying HTTP request object:

const cancel = toHttpTask(request).fork(
  err => console.error(err),
  data => console.log("Success!", data),
);

cancel() // <-- aborts request