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Functional Programming Patterns With RamdaJS!

Inspecting With Tap

Easily trace pipe and compose calls using tap(). (3 min. read)

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One of pipe's potential drawbacks is losing the ability to easily add code for debugging purposes.

Back when we had this

Javascript (babel-node)
const doMath = (num) => {
  const doubled = num * 2;
  const tripled = doubled * 3;
  const squared = tripled * tripled;
  return squared + 1;
}
const result = doMath(2);
console.log({ result });

Jamming a console.log or little hack was easy. How do we inspect piped functions?

Introducing tap. It takes a function, usually a logger, and supplies it the current value. You can do whatever you want without affecting the pipeline since you’re just “tapping” it! :D

Javascript (babel-node)
import { pipe, tap } from 'ramda';
const doMath = pipe(
  tap((num) => {
    console.log('initial number:', num);
  }),
  double,
  tap((num) => {
    console.log('after doubling:', num);
  }),
  triple,
  tap((num) => {
    console.log('after tripling:', num);
  }),
  
  square,
  tap((num) => {
    console.log('after squaring:', num);
  }),
  
  increment,
  tap((num) => {
    console.log('after incrementing:', num);
  }),
);
const result = doMath(2);
console.log({ result });

You don’t even need to use tap itself, just insert a function that returns its arguments unchanged.

Javascript (babel-node)
import { pipe, tap } from 'ramda';
const doMath = pipe(
  (num) => {
    console.log('initial number:', num);
    return num;
  },
  double,
  (num) => {
    console.log('after doubling:', num);
    return num;
  },
  triple,
  (num) => {
    console.log('after tripling:', num);
    return num;
  },
  
  square,
  (num) => {
    console.log('after squaring:', num);
    return num;
  },
  
  increment,
  (num) => {
    console.log('after incrementing:', num);
    return num;
  }
);
const result = doMath(2);
console.log({ result });