Don't invoke trackEvent when tracking data is null or undefined

[williardx]

This change allows us to conditionally track events depending on the return value of the function passed into @track. If the function returns null or undefined then trackEvent will not be invoked.

We've patched this in our own version of react-tracking in order to only track when a user unchecks a box. Example code is below and can be found here.

  @track((props, state, args) => {
    const willInputBillingAddress = !args[0]
    if (willInputBillingAddress) {
      return {
        action_type: Schema.ActionType.Click,
        subject: Schema.Subject.BNMOUseShippingAddress,
        flow: "buy now",
        type: "checkbox",
      }
    }
  })
  handleChangeHideBillingAddress(hideBillingAddress: boolean) {
    ...
  }

[tizmagik]

@williardx I'm wondering if this should be considered a breaking change. E.g. I can imagine someone expecting the following to just work, although probably unlikely (since they'd typically have some sort of { event: "click" } in the handleClick decorator).

@track({ module: 'button' })
class Thing extends Component {
  @track()
  handleClick = () => { ... }

  render() {
    return <button onClick={this.handleClick}>Click me</button>
  }
}

Thoughts?

[williardx]

If I'm reading things correctly, wouldn't that result in calling trackEvent with an empty object since that's the default value for trackingData?

[tizmagik]

It would result in { module: 'button' } being dispatched, since that's defined on context by the decorator on the class.

So while this is technically incorrect usage of react-tracking API, I could see how someone might do the following:

@track({ module: 'button', event: 'click' })
class Thing extends Component {
  @track()
  handleClick = () => { ... }

  render() {
    return <button onClick={this.handleClick}>Click me</button>
  }
}

And actually { module: 'button', event: 'click' } would get dispatched when the button is clicked. So this change may break that, although, again it's kind of incorrect usage of the intended API so I'm leaning towards just making this a minor rather than breaking change.

[alloy]

I think @williardx means that because the default value of trackingData for the method decorator is {} it will still get dispatched. Only examples such as these would not dispatch: @track(null)

[tizmagik]

Oh, yes, I see, I think you're right, because we default it here: https://github.com/NYTimes/react-tracking/blob/aa5fc1aa2a8a871a1b419a5eefbfc38c5b50d77a/src/trackEventMethodDecorator.js#L3

Okay, I feel better about a minor release for this 😁

Thanks again for the PR/feedback guys. Will publish a release now.

[williardx]

Thanks @tizmagik and @alloy!

[tizmagik]

Released v5.6.0

[alloy]

Thanks! ✨