# Types

### Primitive Types

You can use one of primitive types: `*`, `array`, `string`, `undefined`, `boolean`, `function`, `nan`, `null`, `number`, `object`, `regexp`

```javascript
validate( true, "boolean" );
// or
validate( true, "Boolean" );
```

```javascript
validate( null, "boolean" ); // ByContractError: expected boolean but got null

const fn = function(){ validate( arguments, [ "boolean", "*" ]); };
fn( null, "any" ); // ByContractError: Argument #0: expected boolean but got null
```

### Union Types

```javascript
validate( 100, "string|number|boolean" ); // ok
validate( "foo", "string|number|boolean" ); // ok
validate( true, "string|number|boolean" ); // ok
validate( [], "string|number|boolean" );
// ByContractError: expected string|number|boolean but failed on each:
// expected string but got array, expected number but got array, expected boolean but got array
```

### Optional Parameters

```javascript
function foo( bar, baz ) {
  validate( arguments, [ "number=", "string=" ] );
}
foo(); // ok
foo( 100 ); // ok
foo( 100, "baz" ); // ok
foo( 100, 100 ); // ByContractError: Argument #1: expected string but got number
foo( "bar", "baz" ); // ByContractError: Argument #0: expected number but got string
```

### Array Expression

```javascript
validate( [ 1, 1 ], "Array.<number>" ); // ok
validate( [ 1, "1" ], "Array.<number>" );
// ByContractError: array element 1: expected number but got string
// or
validate( [ 1, 1 ], "number[]" ); // ok
validate( [ 1, "1" ], "number[]" );
// ByContractError: array element 1: expected number but got string
```

### Object Expression

```javascript
validate( { foo: "foo", bar: "bar" }, "Object.<string, string>" ); // ok
validate( { foo: "foo", bar: 100 }, "Object.<string, string>" );
// ByContractError: object property bar: expected string but got number
```

### Structure

```javascript
validate({
  foo: "foo",
  bar: 10
}, {
  foo: "string",
  bar: "number"
}); // ok

validate({
  foo: "foo",
  bar: {
    quiz: [10]
  }
}, {
  foo: "string",
  bar: {
    quiz: "number[]"
  }
}); // ok

validate({
  foo: "foo",
  bar: 10
}, {
  foo: "string",
  bar: "number"
}); // ByContractError:  property #bar expected number but got null
```

### Interface validation

You can validate if a supplied value is an instance of a declared interface:

```javascript
class MyClass {}
const instance = new MyClass();

validate( instance, MyClass ); // ok
```

```javascript
class MyClass {}
class Bar {}
const instance = new MyClass();

validate( instance, Bar );
// ByContractError: expected instance of Bar but got instance of MyClass
```

When the interface is globally available you can set contract as a string:

```javascript
const instance = new Date();
validate( instance, "Date" ); // ok

//..
validate( node, "HTMLElement" ); // ok
//..
validate( ev, "Event" ); // ok
```

Globally available interfaces can also be used in Array/Object expressions:

```javascript
validate( [ new Date(), new Date(), new Date() ], "Array.<Date>" ); // ok
```

### Nullable Type

```javascript
validate( 100, "?number" ); // ok
validate( null, "?number" ); // ok
```

### Validation Exceptions

```javascript
import { validate, Exception } from "bycontract";
try {
  validate( 1, "NaN" );
} catch( err ) {
  console.log( err instanceof Error ); // true
  console.log( err instanceof TypeError ); // true
  console.log( err instanceof Exception ); // true
  console.log( err.name ); // ByContractError
  console.log( err.message ); // expected nan but got number
}
```


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