TypeError in Ajax call - php

Question

I'm getting the following error on Ajax call in Laravel 5:
TypeError: 'stepUp' called on an object that does not implement interface HTMLInputElement.
d=[],e=function(a,b){b=n.isFunction(b)?b():null==b?"":b,
The form is as follows:
<form id="comment_form">
<input type="textarea" class="form-control_comment" id="comment" placeholder="Type your comment here...">
<input type="hidden" name="uid" id="uid" value="{{$user->id}}">
<input type="hidden" name="pid" id="pid" value="{{$post->id}}">
<input type="hidden" id="token" value="{{$csrf_token()}}">
<button type="button" class="btn btn-sm btn-success" id= "comment_button">Submit</button>
</form>
The Ajax part:
<script>
$("#comment_button").click(function(e){
e.preventDefault();
var token = $("#token").val();
var a= $("#comment").val();
var uid= $("#uid").val();
var url = "<?php echo Request::root();?>";
$.ajax({
url: url+"post/comment_action",
type: "POST",
async: false,
data: {newComment:a, uid:uid, pid:pid, _token: token},
success: function (newResult){
if(newResult!="")
{
newResult= JSON.parse(newResult);
$("#all_responses").append(newResult);
}
}
}).error(function()
{
alert("Error");
});
});
</script>
in routes.php:
Route::post('post/comment_action', array('as'=>'post/comment_action', 'uses'=>'PostController#postComment_action'));
And the action part in PostController:
public function postComment_action()
{
if(Auth::check())
{
if(Request::ajax())
{
$inputs= Input::all();
}
$new_comment= $inputs['newComment'];
$uid= $inputs['uid'];
$pid= $inputs['pid'];
$com= new Comment;
$com->content= $new_comment;
$com->userId= $uid;
$com->postId= $pid;
$com->save();
$data= array();
$all_comments= Comment::where('postId', $pid)->first();
$u= User::where('id', $uid);
foreach($all_comments as $coms)
{
$data= $coms->content;
}
$data= json_encode($data);
echo $data;
}
else
{
return Redirect::route('signin_user')->withErrors("You must sign in to perform this action");
}
}
Any help would be greatly appreciated :)