Functional Thinking in javascript/nodejs

Question

Functional Thinking in javascript/nodejs

I am a newbie reading about functional thinking in javascript these days. My background is mostly OOP in Java/Ruby.

Suppose I want to get user input in node, I could do it as :

process.stdin.resume();
process.stdin.setEncoding("ascii");
var input_buffer = "";

process.stdin.on("data", function (input) {
  input_buffer += input;
});

function process_input()
{
  // Process input_buffer here.
  do_something_else();
}

function do_something_else()
{

}
process.stdin.on("end",process_input);

I am maintaining explicit state here. What is the functional way to achieve the same thing?

javascript
node.js
functional-programming

Answer 1

Write pure functions for as much of your program as possible
- No I/O, no side effects, no mutable data structures, etc
Keep your I/O cleanly separate and organized

So in general purely functional programmers like to keep their I/O code in a well-contained and small box so they can focus as much as possible on writing pure functions that accept in-memory data types as arguments and return values (or invoke callbacks with values). So with that in mind, the basic idea is:

//Here's a pure function. Does no I/O. No side effects.
//No mutable data structures. Easy to test and mock.
function processSomeData(theData) {
  //useful code here
  return theData + " is now useful";
}

//Here's the "yucky" I/O kept in a small box with a heavy lid
function gatherInput(callback) {
  var input = [];
  process.stdin.on('data', function (chunk) {input.push(chunk);});
  process.stdin.on('end', function () {callback(input.join('');});

}

//Here's the glue to make it all run together
gatherInput(processSomeData);