Add a trace function for debugging functional JS code

global-ramda-trace.js

/*
 * Top level index.js
 */
let R = require('ramda')

global.trace = msg => R.tap(x => console.log(msg, x))

/*
 * ...
 *
 * Somewhere in the app
 *
 */

let R = require('ramda')
let { add, compose, divide, map, multiply, subtract, __ } = R

// Function composition using pointfree style
let performComplexCalc = compose(subtract(__, 2), divide(__, 4), multiply(10), add(10))

// Maybe there's a bug in our function, but where?
map(performComplexCalc, [1, 2, 3, 4, 5])

// To trace through steps, just spinkle `trace` calls in the composition
performComplexCalc = compose(
  trace('after'),
  subtract(__, 2),
  divide(__, 4),
  trace('middle'),
  multiply(10),
  add(10),
  trace('before'))
  
// This way we don't have to resort to changing function to this
performComplexCalc = (x) => {
  console.log('before', x)
  let result = add(10, x)
  result = multiply(10, result)
  console.log('middle', result)
  result = divide(result, 4)
  result = subtract(result, 2)
  console.log('after', result)
  return result
}

Also see @raine's treis.