debian-mirror-gitlab/doc/development/event_tracking/frontend.md

Frontend tracking guide

GitLab provides Tracking, an interface that wraps the Snowplow Javascript Tracker for tracking custom events. There are a few ways to utilizing tracking, but each generally requires at minimum, a category and an action. Additional data can be provided that adheres to our Feature instrumentation taxonomy.

field	type	default value	description
category	string	document.body.dataset.page	Page or subsection of a page that events are being captured within.
action	string	'generic'	Action the user is taking. Clicks should be click and activations should be activate, so for example, focusing a form field would be activate_form_input, and clicking a button would be click_button.
data	object	{}	Additional data such as label, property, value, and context as described in our Feature Instrumentation taxonomy.

Tracking in HAML (or Vue Templates)

When working within HAML (or Vue templates) we can add data-track-* attributes to elements of interest. All elements that have a data-track-event attribute will automatically have event tracking bound on clicks.

Below is an example of data-track-* attributes assigned to a button:

%button.btn{ data: { track: { event: "click_button", label: "template_preview", property: "my-template" } } }

<button class="btn"
  data-track-event="click_button"
  data-track-label="template_preview"
  data-track-property="my-template"
/>

Event listeners are bound at the document level to handle click events on or within elements with these data attributes. This allows for them to be properly handled on rerendering and changes to the DOM, but it's important to know that because of the way these events are bound, click events shouldn't be stopped from propagating up the DOM tree. If for any reason click events are being stopped from propagating, you'll need to implement your own listeners and follow the instructions in Tracking in raw Javascript.

Below is a list of supported data-track-* attributes:

attribute	required	description
data-track-event	true	Action the user is taking. Clicks must be prepended with click and activations must be prepended with activate. For example, focusing a form field would be activate_form_input and clicking a button would be click_button.
data-track-label	false	The label as described in our Feature Instrumentation taxonomy.
data-track-property	false	The property as described in our Feature Instrumentation taxonomy.
data-track-value	false	The value as described in our Feature Instrumentation taxonomy. If omitted, this will be the elements value property or an empty string. For checkboxes, the default value will be the element's checked attribute or false when unchecked.
data-track-context	false	The context as described in our Feature Instrumentation taxonomy.

Tracking within Vue components

There's a tracking Vue mixin that can be used in components if more complex tracking is required. To use it, first import the Tracking library and request a mixin.

import Tracking from '~/tracking';
const trackingMixin = Tracking.mixin({ label: 'right_sidebar' });

You can provide default options that will be passed along whenever an event is tracked from within your component. For instance, if all events within a component should be tracked with a given label, you can provide one at this time. Available defaults are category, label, property, and value. If no category is specified, document.body.dataset.page is used as the default.

You can then use the mixin normally in your component with the mixin, Vue declaration. The mixin also provides the ability to specify tracking options in data or computed. These will override any defaults and allows the values to be dynamic from props, or based on state.

export default {
  mixins: [trackingMixin],
  // ...[component implementation]...
  data() {
    return {
      expanded: false,
      tracking: {
        label: 'left_sidebar'
      }
    };
  },
}

The mixin provides a track method that can be called within the template, or from component methods. An example of the whole implementation might look like the following.

export default {
  mixins: [Tracking.mixin({ label: 'right_sidebar' })],
  data() {
    return {
      expanded: false,
    };
  },
  methods: {
    toggle() {
      this.expanded = !this.expanded;
      this.track('click_toggle', { value: this.expanded })
    }
  }
};

And if needed within the template, you can use the track method directly as well.

<template>
  <div>
    <a class="toggle" @click.prevent="toggle">Toggle</a>
    <div v-if="expanded">
      <p>Hello world!</p>
      <a @click.prevent="track('click_action')">Track an event</a>
    </div>
  </div>
</template>

Tracking in raw Javascript

Custom event tracking and instrumentation can be added by directly calling the Tracking.event static function. The following example demonstrates tracking a click on a button by calling Tracking.event manually.

import Tracking from `~/tracking`;

const button = document.getElementById('create_from_template_button');
button.addEventListener('click', () => {
  Tracking.event('dashboard:projects:index', 'click_button', {
    label: 'create_from_template',
    property: 'template_preview',
    value: 'rails',
  });
})

Tests and test helpers

In Karma tests, you can use the following:

import { mockTracking, triggerEvent } from 'spec/helpers/tracking_helper';

describe('my component', () => {
  let trackingSpy;
  
  beforeEach(() => {
    const vm = mountComponent(MyComponent);
    trackingSpy = mockTracking('_category_', vm.$el, spyOn);
  });
  
  it('tracks an event when toggled', () => {
    triggerEvent('a.toggle');

    expect(trackingSpy).toHaveBeenCalledWith('_category_', 'click_edit_button', {
      label: 'right_sidebar',
      property: 'confidentiality',
    });
  });
});