metamask-extension/docs/creating-metrics-events.md

## Creating Metrics Events

The `metricsEvent` method is made available to all components via context. This is done in `metamask-extension/ui/app/helpers/higher-order-components/metametrics/metametrics.provider.js`. As such, it can be called in all components by first adding it to the context proptypes:

```
static contextTypes = {
  t: PropTypes.func,
  metricsEvent: PropTypes.func,
}
```

and then accessing it on `this.context`.

Below is an example of a metrics event call:

```
this.context.metricsEvent({
  eventOpts: {
    category: 'Navigation',
    action: 'Main Menu',
    name: 'Switched Account',
  },
})
```

### Base Schema

Every `metricsEvent` call is passed an object that must have an `eventOpts` property. This property is an object that itself must have three properties:
- category: categorizes events according to the schema we have set up in our matomo.org instance
- action: usually describes the page on which the event takes place, or sometimes a significant subsections of a page
- name: a very specific descriptor of the event

### Implicit properties

All metrics events send the following data when called:
- network
- environmentType
- activeCurrency
- accountType
- numberOfTokens
- numberOfAccounts

These are added to the metrics event via the metametrics provider.

### Custom Variables

Metrics events can include custom variables. These are included within the `customVariables` property that is a first-level property within first param passed to `metricsEvent`.

For example:
```
this.context.metricsEvent({
  eventOpts: {
    category: 'Settings',
    action: 'Custom RPC',
    name: 'Error',
  },
  customVariables: {
    networkId: newRpc,
    chainId,
  },
})
```

Custom variables can have custom property names and values can be strings or numbers.

**To include a custom variable, there are a set of necessary steps you must take.**

1. First you must declare a constant equal to the desired name of the custom variable property in `metamask-extension/ui/app/helpers/utils/metametrics.util.js` under `//Custom Variable Declarations`
1. Then you must add that name to the `customVariableNameIdMap` declaration
    1. The id must be between 1 and 5
    1. There can be no more than 5 custom variables assigned ids on a given url