How do I pass a route parameter to Vue.js from Laravel

I have a route like this to fetch a post with the associated comment.

Route::get('/api/topics/{category_id}/{title}', function($category_id, $title){
    return App\Topic::with('comments')->where(compact('category_id','title'))->firstOrFail();
});

The thing is how can I pass a parameter variables to Vue.js?In this case "category_id" and "title",so Vue can fetch the post as well as the comments.

Below is my Vue instance which gives me this error:

main.js:11749Uncaught ReferenceError: category_id is not defined

Vue instance

new Vue({


el: '#comment',

methods: {

    fetchComment: function (category_id, title) {
        this.$http.get('/api/topics/' + category_id + '/' + title ,function (data) {
            this.$set('topics',data)
        })
    }


},
ready: function () {
    this.fetchComment(category_id, title)
}
}); 

via Chebli Mohamed