middleware_1.js

let step = null;

const middleware = store => next => action => {
  switch (action.type) {
  case 'SET_ONBOARDING_STEP':
    step = action.payload;
    const { url } = steps[step];
    // Make sure we "replace" instead of "push" when we have an on-boarding
    // exclusive URL.
    const redirectMethod = exclusiveUrls.indexOf(url) >= 0 ? replace : push;
    store.dispatch( redirectMethod(url) );
    break;
  case 'ADD_ONBOARDING_MILESTONE':
    milestones.push(action.payload);
    break;
  case 'REMOVE_ONBOARDING_MILESTONE':
    const idx = milestones.indexOf(action.payload);
    if (idx >= 0) milestones.splice(idx, 1);
    break;
  case 'INSERT_ONBOARDING_STEP':
    const { stepBefore, step, stepLabel } = action.payload;
    steps[stepBefore].nextStep = stepLabel;
    steps[stepLabel] = step;
    break;
  case 'REMOVE_ONBOARDING_STEP':
    const { stepLabel, newNextStep } = action.payload;
    
    // Rewrite all pointers to the deleted step with the new next step label.
    Object.keys(steps).forEach((label) => {
      if (steps[label].nextStep === stepLabel) steps[label].nextStep = newNextStep;
    });
    delete steps[stepLabel];
    break;
  case 'SET_FINAL_ONBOARDIND_ACTION':
    finalAction = action.payload;
    break;
  }
};