jquery undefined function

Hi all 

I try to call a javascript function from a separate file, it gives me an undefined function:

I used this code in the blade file and included the js file at the bottom of the blade file 

select name=service_id id="service_id" onChange="displaycategories(this.value)">

<script src="{{ asset('js/services.js') }}"></script>

in the service.js file I have the displaycategories function

$(document).ready(function() { function displaycategories(name) { // CODE }});

it gives me this error

Uncaught ReferenceError: displaycategories is not defined at HTMLSelectElement.onchange (760232:303:74)