jquery - javascript read file object unknown id -

is possible use javascript file api read file object of unknown id?

i use custom file upload form in code doesn't have input element. uses plupload.js api , can't determine how access contents of file object.

for example if code had line 1, access contents of file object using code of line 2

1. input type="file" id="data"
2. var finput = document.getelementbyid("data"); var f = finput.files[0];

i tried document.files[0] doesn't work. know similar?

instead of document.files[0], try document.queryselectorall('input[type="file"]')[0].

function demo(){    var inpts=document.queryselectorall('input[type="file"]');    alert(inpts[0].classname);  }

<input type="file" class="file_input_a"><br>  <input type="file" class="file_input_b"><br>  <input type="file" class="file_input_b"><br>  <button onclick="demo()">demo</button>

the above example echo's classname of file-input 0 (to show have reference it).
here on want grab (for example) first file (from first found input-element):

var f = inpts[0].files[0]; 

^{ps: there lot of related info in answer linked here.}