understanding es6 pipeline O|>erator

Pipeline operator |> is a readable way of writing chained functions. The operator is currently at stage 1 of tc39 proposal (ESNext Proposal).

The pipeline operator provides a syntactic sugar to call a function with single argument.

expression |> function 

//or call multiple functions as 

expression |> fn1 |> fn2 |> fn3

each function gets the result from its preceeding function as input and passes the result to next function i.e. input (argument/expression) is piped through and complete pipeline.

Let’s look at some examples :

Define the double and increment functions to use in examples.

const double = n => n * 2; 

const increment = n => n + 1;

The function(argument) way:

We can call functions as g(f(n)) to get our input parameter n through the functions f(n) and g(m). OR by taking intermediate value as a variable: var a = f(n); result = g(a):

double(increment(double(10)));  //42

// OR

let a = double(10); //20

let b = increment(a); //21

let result = double(b); //42

using lodash

Using lodash we can achieve the same (chaining) by using _.chain() for inbuilt methods or by _.mixin() for using custom methods or by _.flow() (functional compositions).

const _ = require('lodash');

// using lodash mixin

_.mixin({'double': double, 'increment': increment});

_(10).double().increment().double().value(); //42

// using lodash flow

const doubleIncrementDouble = _.flow([double, increment, double]);

let result = doubleIncrementDouble(10) //42

es5 utility function

To write a utility function to do the same for us, we need to define a function (pipe) that takes a list (array) of methods (functions) and returns a function which takes only one parameter and reduces the functions array from its parent scope initializing with its parameter.
Now as we have a wrapper function pipe we can call it as pipe([fn1, fn2, f3 ...fm])(n) or we can define different pipes taking list of functions var pipeline1 = [double, increment] and then call it as pipeline1(a).

//  pipeline utility

var pipe = function (functionList) {

  return function (data) {

    return functionList.reduce(function(value, func) {
      return func(value)
    }, data);

  }

}

pipe([double, increment, double])(10); //42

ESNext pipeline operator 10 |> double |> increment |> double;

As we often need to transform some data or clean data for some usages like data visualizations , tabular representations, payload generations etc. we need a utility or use a library like lodash for doing that part only, it is good to have feature in language itself as similar to [F#](https://en.wikibooks.org/wiki/F Sharp_Programming/Higher_Order_Functions#The.7C.3E_Operator), OCaml, Elixir, Elm, Julia, Hack, LiveScript, as well as UNIX pipes.

Also as in proposal :

…you can use an arrow function to handle multi-argument functions.

Thank You !!

Your thoughts , suggestions or corrections are most welcome !!, Please feel free to share them below. will test some more complex examples and will share If I found anything interesting.

References :

ESNext Proposal tc39

MDN web docs

Raw code

Gist