Extract a method chain in Javascript?

Question

Given a function which performs a set of operations

const addSum = arr => arr.map(i => i+1).filter(i => i % 2 !== 0).map(i => i+1)

Is there a way to extract the method chain? For example, get a tree of the operations performed in an object like

{map: {filter: "map"}}

Edit: Updated example

Answer 1

You could save the name of the extension methods and the callback in a 2D array. Then use reduce to call each function one by one and return the result as accumulator in each iteration

const sequence = (initial, ops) => ops.reduce((acc, [f, cb]) => acc[f](cb), initial)

// Save each opeartion in: ["extension name", callback] format
const operations = [
  ['map', i => i + 1],
  ['filter', i => i % 2],
  ['map', i => i + 2]
]

const output = sequence([1, 2, 3], operations)

console.log(output)

Or, you could use a pipe function used in functional pattern

const increment = n => arr => arr.map(i => i + n)
const evenFilter = arr => arr.filter(i => i % 2)

function pipe(...fns) {
  return arg => fns.reduce((prev, fn) => fn(prev), arg);
}

console.log(
  pipe(increment(1), evenFilter, increment(2))([1, 2, 3])
)