I'm learning Ramda and try to reach pointfree programming. In order to do that, I try to refactor here and there but got stuck on this.

I obviously think this doesn't work because the call is asychronous but I could not find what is wrong with this code.

// Why is this
const toJSONRamda = R.pipe(
  R.prop('json'), // getting the 'json' function
  R.call // and calling it
)

// different from this
const toJSON = response => response.json()

// Works
fetch('')
  .then(toJSON)
  .then(console.log)
  
// Does not Work
fetch('')
  .then(toJSONRamda)
  .then(console.log)

<script src=".25.0/ramda.min.js"></script>

I'm learning Ramda and try to reach pointfree programming. In order to do that, I try to refactor here and there but got stuck on this.

I obviously think this doesn't work because the call is asychronous but I could not find what is wrong with this code.

// Why is this
const toJSONRamda = R.pipe(
  R.prop('json'), // getting the 'json' function
  R.call // and calling it
)

// different from this
const toJSON = response => response.json()

// Works
fetch('https://jsonplaceholder.typicode./todos/1')
  .then(toJSON)
  .then(console.log)
  
// Does not Work
fetch('https://jsonplaceholder.typicode./todos/1')
  .then(toJSONRamda)
  .then(console.log)

<script src="https://cdnjs.cloudflare./ajax/libs/ramda/0.25.0/ramda.min.js"></script>

• javascript
• promise
• functional-programming
• fetch-api
• ramda.js

1 Answer 1

The reason this doesn't work is that the json method of the response object is not a pure function. It is really a method. When you use pipe(prop('json'), call), you are trying to call that method as a pure function. In some circumstances that will work. But here, the json method actually uses this. Ramda's call does not supply any this object.

There is a Ramda alternative:

const toJSONRamda = R.invoker(0, 'json')

fetch('https://jsonplaceholder.typicode./todos/1')
  .then(toJSONRamda)
  .then(console.log)

<script src="//cdnjs.cloudflare./ajax/libs/ramda/0.25.0/ramda.js"></script>

invoker works with methods. These should help describe how it works:

R.invoker(0, 'method')(obj) = obj['method']()
R.invoker(1, 'method')(a, obj) = obj['method'](a)
R.invoker(2, 'method')(a, b, obj) = obj['method'](a, b)
//...

However, there is an important point not to miss. Point-free programming is useful only so long as it improves readability. This to me is already perfectly readable:

fetch('https://jsonplaceholder.typicode./todos/1')
  .then(resp => resp.json())
  .then(console.log)

If this is only a learning exercise, then, by all means feel free to try to turn that into a point-free version. But I would leave it as is for production code.