> For the complete documentation index, see [llms.txt](https://docs.activejs.dev/activejs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.activejs.dev/activejs/fundamentals/units/numunit.md).

# NumUnit

**NumUnit** is a type of [Unit](/activejs/fundamentals/units.md) that only accepts `number` data type as its value. It ensures that at any point of time the value would always be `number`.
 It doesn't even accept `NaN` as it's value.

It implements all the [Number.prototype](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number) methods available in the environment/browser, including polyfills.\
e.g.:`toFixed` and `toString`
, and redirects them to the stored `number` value inside the Unit, so when you call `Unit.toString()` , it'll be executed on the Unit's value instead of the NumUnit instance itself.

See [API reference](https://api.activejs.dev/classes/numunit) for more details.

|                 |          |
| --------------- | -------- |
| Default value   | `0`      |
| Value data type | `number` |

### NumUnit vs `number`

NumUnit can not be used as a drop-in replacement for primitive `number` value, since NumUnit is a non-primitive data structure, and the actual `number` value is stored inside the Unit. See the below comparisons for more clarity.

```typescript
// initialization
let num = 42069; // a variable with prmitive number value
const unit = new NumUnit({initialValue: 42069});
// initialValue is optional, NumUnit has 0 as default value

num === unit // false
num === unit.value() // true

num.toString() // '42069'
numUnit.toString() // '42069'

num.toLocaleString() // '42,069' (in an 'en' locale)
numUnit.toLocaleString() // '42,069' (in an 'en' locale)

num + 1 // 42070
numUnit + 1 // 42070 // this doesn't change the Unit's value

num + 'XX' // '42069XX'
numUnit + 'XX' // '42069XX' // this doesn't change the Unit's value

typeof num === 'number' // true
typeof unit === 'object' // true
typeof unit.value() === 'number' // true

// value assignment
num = 7;
unit.dispatch(7);

// value access
console.log(num) // logs 7
console.log(unit.value()) // logs 7
// or
unit.subscribe(value => console.log(value)) // logs 7, will log future values
```