Blade does not accept variable

This is my code

var feetype="";
console.log(feetype);

Works perfectly fine. However when I try to modify it like so

var fee_type_id = 2;
var feetype="";
console.log(feetype);

It throws the following error

Use of undefined constant fee_type_id - assumed 'fee_type_id' (this will throw an Error in a future version of PHP)

What am I doing wrong?

via Chebli Mohamed