Find failed build task in Circle build - Zapier function

circleZapier.js

fetchBuild(inputData.buildNum, CIRCLE_TOKEN)
  .then(failedAction)
  .then(function(action) {callback(null, {'Failed Action': action})})
  .catch(function(err) {callback(err)})

function fetchBuild(buildNum, circleToken) {
  return fetch(
    'https://circleci.com/api/v1.1/project/github/cucumber-ltd/cucumber-pro/' +
      buildNum +
      '?circle-token=' +
      circleToken
  ).then(function(res) {return res.json()})
}

function failedAction(build) {
  var step = build.steps.find(function(step) {
    return step.actions.find(function(action) {
      return action.exit_code && action.exit_code !== 0
    })
  })
  return step ? step.name : null
}