how to get all checkboxes from one of three forms?

I have an three forms, each of them has checkboxes and submit button, need to get all checkbox name or id by clicking on submit button only this form. And for other two also.

function getCheckedBoxes(item) {
var checkboxes = document.getElementsByName(item);
var checkboxesChecked = [];
// loop over them all
for (var i=0; i<checkboxes.length; i++) {
    // And stick the checked ones onto an array...
    if (checkboxes[i].checked) {
        checkboxesChecked.push(checkboxes[i]);
    }
}
// Return the array if it is non-empty, or null
console.log(checkboxes);
return checkboxesChecked.length > 0 ? checkboxesChecked : null;
}


var inp = document.getElementsByName('send');
for(var i = 0; i < inp.length; i++){
inp[i].addEventListener('click', function(e) {
    getCheckedBoxes("item");

    e.preventDefault();
});
}

example of my checkboxes

 <form>
 <input id="check29" type="checkbox" name="item" value="29" />
 <input class="lab-btn" type="submit" value="ADD ALL" name="send">
 </form>