Problema com js

categories.blade.php

@extends('layouts.admin-master')

@section('styles')
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css" />
    <link rel="stylesheet" href="{{URL::to('src/css/categories.css')}}" type="text/javascript" />
@endsection

@section('content')
    <div class="container">
        <section id="category-admin">
            <form action="" method="post">
                <div class="input-group">
                    <label for="name">Nome da categoria</label>
                    <input type="text" name="name" id="name" />
                    <button class="btn">Criar categoria</button>
                </div>
            </form>
        </section>
        <section class="list">
            @foreach($categories as $category)
                <article>
                    <div class="category-info" data-id="{{$category->id}}">
                        <h3>{{ $category->name }}</h3>
                    </div>
                    <div class="edit">
                        <nav>
                            <ul>
                                <li class="category-edit"><input type="text" /></li>
                                <li><a href="#">Editar</a></li>
                                <li><a href="#">Excluir</a></li>
                            </ul>
                        </nav>
                    </div>
                </article>
            @endforeach
        </section>
    </div>
    @if($categories->lastPage() > 1)
        <section class="paginacao">
            @if($categories->currentPage() !== 1)
                <a href="{{ $categories->previousPageUrl() }}"><i class="fa fa-caret-left"></i></a>
            @endif
            @if($categories->currentPage() !== $categories->lastPage())
                <a href="{{ $categories->nextPageUrl() }}"><i class="fa fa-caret-right"></i></a>
            @endif
        </section>
    @endif
@endsection

@section('scripts')
    <script type="text/javascript">
        var token = "{{ Session::token() }}";
    </script>
    <script type="text/javascript" src="{{URL::asset('src/js/categories.js')}}"></script>
@endsection

categories.js

var docReady = setInterval(function () {
    if (document.readyState !== "complete") {
        return;
    }
    clearInterval(docReady);

    document.getElementsByClassName('btn')[0].addEventListener('click', createNewCategory);
}, 100);

function createNewCategory(event) {
    event.preventDefault();
    var name = event.target.previousElementSibling.value;
    if (name.length === 0) {
        alert("Por favor, digite um nome para categoria");
        return;
    }
    
    ajax("POST", "/admin/blog/category/create", "name=" + name, newCategoryCreated, [name]);
}

function newCategoryCreated(params, success, responseObj) {
    location.reload();
}

function ajax(method, url, params, callback, callbackParams) {
    var http;
    
    if (window.XMLHttpRequest) {
        http = new XMLHttpRequest();        
    } else {
        http = new ActiveXObject("Microsoft.XMLHTTP");
    }

    http.onreadystatechange = function() {
        if(http.readyState == XMLHttpRequest.DONE){
            if(http.status == 200){
                var obj = JSON.parse(http.responseText);
                callback(callbackParams, true, obj);
            }else if(http.status == 400){
                alert('deu merdss');
                callback(callbackParams, false);
            }else{
                var obj = JSON.parse(http.responseText);
                if(obj.message){
                    alert(obj.message);
                }else{
                    alert('deu merdss 2');
                }
            }
        }
    };
    
    http.open(method, baseUrl + url, true);
    http.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    http.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
    http.send(params + "&_token=" + token);
}