Why can't request get the value passed by ajax?

Question

ajax part:

$.ajax({
type:"post",
url:"{:url('Contact/sendEmail')}",
data: "username=" $("#username").val(),
//dataType:'json',
success: function (data) {
alert(data);
}
})

thinkphp part:

//Send email
public function sendEmail(Request $request){
$data = $request->param(); //Return information
$name = $data['username'];

Supplement: There is no problem with the path, and request

is also used to report error:

Not yet Define array index: username

Answer 1

data:{

'username' : $("#username").val()

}

In ajax, data is replaced with an object ? ? ?

Answer 2

manual

Answer 3

1. Is there a value in Form Data

1. 
   

2. # # request whether to use