Task

Task represent values that depend on time similar to Promise. But Task are lazy and monadic by design, the value will not there until you ask it, by calling .fork method.

It allow us to compose and sequence time-dependent effects using the generic and powerful monadic operations.

function getRequest(path) {
  return new Task((error, success) => {
    let xhr = new XMLHttpRequest()
    xhr.onerror = () => {
      error(new TypeError('Network request failed'))
    }
    xhr.ontimeout  = () => {
      error(new TypeError('Network request timeout'))
    }
    xhr.onload = () => {
      let body = 'response' in xhr ? xhr.response : xhr.responseText
      success(body)
    }
  })
}

function parseJson(request) {
  return request.map(body => Json.parse(body))
}

parseJson(getRequest('/target-url'))
.fork((error) => {
  // something wrong happen
}, (result) => {
  console.log(result);
})