# Using the Analytics.js Querystring API

Analytics.js can trigger Track and Identify events based on the URL query string. You can use this when tracking email click-throughs, social media clicks, and digital advertising.

Here are the *optional* query parameters to use:

| Parameter             | Description                             | Triggers                                                                                                                                        |
| --------------------- | --------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------- |
| `ajs_uid`             | The userId to pass to an Identify call. | This triggers an Identify call.                                                                                                                 |
| `ajs_event`           | The event name to pass to a Track call. | This triggers a Track call.                                                                                                                     |
| `ajs_aid`             | The `anonymousId` to set for the user.  | This function returns the current `anonymousId`. When a value is passed, this function sets an `anonymousId` value.                             |
| `ajs_prop_<property>` | A property to pass to the Track call.   | This won't implicitly trigger an event and is dependent on you also passing `ajs_event`. This property is included in the resulting Track call. |
| `ajs_trait_<trait>`   | A trait to pass to the Identify call.   | This won't implicitly trigger any call and is dependent on you also passing `ajs_uid`. This trait is included in the resulting Identify call.   |

For example, this URL creates the following events on the page:

```text
http://segment.com/?ajs_uid=123456789abcd&ajs_event=Clicked%20Email&ajs_aid=abc123&ajs_prop_emailCampaign=First+Touch&ajs_trait_name=Karl+Jr.
```

Each trigger parameter is optional. You can pass up to **1 of each trigger parameter**, as shown in the following example:

```js
analytics.identify('123456789abcd', { name: 'Karl Jr.' });
analytics.track('Clicked Email', { 'emailCampaign': 'First Touch' });
analytics.user().anonymousId('abc123');
```

## How can I control query string processing?

The `useQueryString` option allows you to control the behavior of the query parameters. For example, you can entirely disable query string processing by setting `useQueryString` to `false`:

```js
analytics.load('<WRITE_KEY>', {
  useQueryString: false
})
```

You can also keep query string processing on, but enforce validation rules. For example:

```js
analytics.load('<WRITE_KEY>', {
  useQueryString: {
    // set a pattern for anonymousId 
    aid: /([A-Z]{10})/,
    // set a pattern for userId
    uid: /([A-Z]{6})/
  }
})
```