# StringUnit

**StringUnit** is a type of [Unit](https://docs.activejs.dev/activejs/fundamentals/units) that only accepts `string` data type as its value. It ensures that at any point of time the value would always be `string`.

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

When we use `String.prototype` methods like `replace`, it doesn't mutate the value of the Unit, similar to how simple `String.prototype.replace` works.

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

|                 |                     |
| --------------- | ------------------- |
| Default value   | `''` (empty string) |
| Value data type | `string`            |

### StringUnit vs `string`

StringUnit can not be used as a drop-in replacement for primitive `string` value, since StringUnit is a non-primitive data structure, and the actual `string` value is stored inside the Unit, which can be accessed via`Unit.value()` method. See the below comparisons for more clarity.

```typescript
// initialization
let str = 'Hello';
const unit = new StringUnit({initialValue: 'Hello'});

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

unit + ' World' // 'Hello World'
unit + 1 // 'Hello1'
unit.dispatch('6');
parseInt(unit) // 6

typeof str === 'string' // true
typeof unit === 'object' // true
typeof unit.value() === 'string' // true

// value assignment
str = 'bye';
unit.dispatch('bye');

// value access
console.log(str) // logs 'bye'
console.log(unit.value()) // logs 'bye'
// OR
unit.subscribe(value => console.log(value)) // logs 'bye', will log future values
```


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