Select element base on name with jQuery

Question

My form has fields like this:

<input type="text" class="form-control" name="item_1[firstname]">
<input type="text" class="form-control" name="item_2[firstname]">
<input type="text" class="form-control" name="item_3[firstname]">

How can I select them with jQuery ?

What I tried :

$('input[name="item_^[firstname]"]').length();

Note: I do not want to change the structure and select element by another way (only by name).

Thanks.