diff.js

const {diffChars} = require('diff')
const c = require('ansi-colors')
const Result = require('folktale/result')

module.exports = ({ expected, value }) => (
  expected === value
    ? Result.Ok()
    : Result.Error(
      c.red('- expected  ') + c.green('+ actual\n') +
      diffChars(expected, value)
        .map(change => (
          change.added
            ? c.green(change.value)
            : change.removed
              ? c.red(change.value)
              : change.value
        ))
        .join('')
    )
)