# Trackers

Trackers track the value(s) of something. Anything, really.
A tracker does this **every hour or every day**.
Once a tracker tracks an event, **it sends it to our databases** to be **saved for up to a month**.

Trackers are used to easily show statistics without having to manage the data yourself.

## Example

```js
const kontrl = require("kontrl");

// This tracker counts the rows of the users table (see tables documentation)
const myUserTracker = kontrl.tracker.countResources({
  resourceNames: ["users"],
  precision: "hour" // Can be once an hour or once a day.
});
```

There are a few **premade trackers**. It's also possible to **make your own** trackers.

## Premade trackers

- **events** Uses custom events to make a graph (see Events documentation).
- **countResource** Tracks how many items there are in a table
- **custom trackers** See the "Custom trackers" section.

## Events tracker

When you throw events, (see Events page), you can make a tracker to display this data on the dashboard.

**Params:**

- **eventName** the name of the events. (see Events page).

```js
const kontrl = require("kontrl");

const routeVisitsTracker = kontrl.tracker.events({
  eventName: "route_visits"
});
```

## Count Resources tracking

A simple premade tracker the items of 1 or more tables. (see Tables page).

**Params:**

- **resourceNames** an array of 1 or more table names.
- **precision** how often you want to track. can be "hour" or "day".

```js
const kontrl = require("kontrl");

const userCountTracker = kontrl.tracker.countResources({
  resourceNames: ["users"],
  precision: "hour"
})
```

## Custom trackers

It's incredibly easy to write your own trackers.

First, decide whether you want to track a single number or multiple numbers at the same time.

### Tracking a single value

You track a single value by using the **kontrl.tracker.single(..)** function. 

**Params:**

- **uniqueName** the name of what are tracking. Unique within your application and maximum 20 characters long.
- **precision** the interval at which the value will get tracked. Can be "hour" or "day" meaning hourly and daily respectively.
- **getValue** the function which will be called every hour or day that gets the value. This function expects a single number as a return

```js
const kontr = require("kontrl");

kontrl.tracker.single({
  uniqueName: "new_users_today",
  precision: "day",
  getValue() {
    const newUserCount = 100; // get the data from your database
    return newUserCount;
  }
})
```

### Tracking multiple values

You track a combination of values using the **kontrl.tracker.many(..)** function.

**Params:**

- **uniqueName** the name of what are tracking. Unique within your application and maximum 20 characters long.
- **precision** the interval at which the value will get tracked. Can be "hour" or "day" meaning hourly and daily respectively.
- **getValue** the function that gets the value. This function **returns an object**.

```js
const kontr = require("kontrl");

kontrl.tracker.many({
  uniqueName: "stock",
  precision: "day",
  getValues() {
    // Get the current stock items
    const itemsInStock = { "gameboy": 3, "Pokemon fire red": 9 };
    return itemsInStock;
  }
})
```