# HasInstanceSymbol
> Has instance [symbol][mdn-symbol] which is used to determine if a constructor object recognizes an object as its instance.
## Usage
```javascript
var HasInstanceSymbol = require( '@stdlib/symbol/has-instance' );
```
#### HasInstanceSymbol
Has instance [`symbol`][mdn-symbol] which is used to determine if a constructor object recognizes an object as its instance.
```javascript
var s = typeof HasInstanceSymbol;
// e.g., returns 'symbol'
```
## Notes
- The [symbol][mdn-symbol] is only supported in environments which support [symbols][mdn-symbol]. In non-supporting environments, the value is `null`.
- The `instanceof` operator uses the following algorithm to determine the return value of `object instanceof constructor`:
- If `constructor` has a `[HasInstanceSymbol]()` method, the `instanceof` operator calls the method with `object` as the first argument and returns the result (coerced to a boolean). If `constructor` is not an object or if `constructor[HasInstanceSymbol]` is neither `null`, `undefined`, nor a function, the `instanceof` operator raises an exception.
- Otherwise, if `constructor` does not have a `[HasInstanceSymbol]()` method (i.e., `constructor[HasInstanceSymbol]` is `null` or `undefined`), the `instanceof` operator determines the result using the same algorithm as `Function.prototype[HasInstanceSymbol]()`. If `constructor` is not a function, the `instanceof` operator raises an exception.
## Examples
```javascript
var isArray = require( '@stdlib/assert/is-array' );
var instanceOf = require( '@stdlib/assert/instance-of' );
var defineProperty = require( '@stdlib/utils/define-property' );
var HasInstanceSymbol = require( '@stdlib/symbol/has-instance' );
function ArrayLike() {
return {
'length': 3,
'0': 4,
'1': 5,
'2': 6
};
}
function hasInstance( instance ) {
return isArray( instance );
}
var x = [ 1, 2, 3 ];
defineProperty( ArrayLike, HasInstanceSymbol, {
'configurable': true,
'value': null
});
console.log( instanceOf( x, ArrayLike ) );
defineProperty( ArrayLike, HasInstanceSymbol, {
'configurable': true,
'value': hasInstance
});
console.log( instanceOf( x, ArrayLike ) );
```
[mdn-symbol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol