# Function Name
> Determine a function's name.
## Usage
```javascript
var functionName = require( '@stdlib/utils/function-name' );
```
#### functionName( fcn )
Returns the name of a `function`.
```javascript
var v = functionName( Math.sqrt );
// returns 'sqrt'
```
If provided an **anonymous** `function`, the function returns an empty `string` or the string `"anonymous"`.
```javascript
var v = functionName( function () {} );
// returns '' || 'anonymous'
```
If provided a value which is not a `function`, the function **throws** a `TypeError`.
```javascript
try {
functionName( 'beep' );
// throws error...
} catch ( err ) {
console.error( err );
}
```
## Notes
- For more information regarding the naming of anonymous functions, see
- [Function Names in ES6][2ality-function-names]
- Webkit bug [7726][webkit-bug-7726]
- [MDN][mdn-function-name]
## Examples
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var Buffer = require( '@stdlib/buffer/ctor' );
var Number = require( '@stdlib/number/ctor' );
var functionName = require( '@stdlib/utils/function-name' );
var v = functionName( Math.sqrt );
// returns 'sqrt'
v = functionName( Float64Array );
// returns 'Float64Array'
v = functionName( Buffer );
// returns 'Buffer'
v = functionName( Date );
// returns 'Date'
v = functionName( String );
// returns 'String'
v = functionName( Boolean );
// returns 'Boolean'
v = functionName( Function );
// returns 'Function'
v = functionName( Number );
// returns 'Number'
v = functionName( function foo() {} );
// returns 'foo'
v = functionName( function () {} );
// returns '' || 'anonymous'
```
[2ality-function-names]: http://www.2ality.com/2015/09/function-names-es6.html
[webkit-bug-7726]: https://bugs.webkit.org/show_bug.cgi?id=7726
[mdn-function-name]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name