How to get all checked checkboxes

I have a set of input checkboxes with the same name and I would like to determine which checkboxes have been checked using javascript, how can I achieve that? I know only how to get all the checkboxes as follows:

var checkboxes = document.getElementsByName('mycheckboxes');

In IE9+, Chrome or Firefox you can do:

var checkedBoxes = document.querySelectorAll('input[name=mycheckboxes]:checked');

A simple for loop which tests the checked property and appends the checked ones to a separate array. From there, you can process the array of checkboxesChecked further if needed.

// Pass the checkbox name to the function
function getCheckedBoxes(chkboxName) {
  var checkboxes = document.getElementsByName(chkboxName);
  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
  return checkboxesChecked.length > 0 ? checkboxesChecked : null;
}

// Call as
var checkedBoxes = getCheckedBoxes("mycheckboxes");

For a simple two- (or one) liner this code can be:

checkboxes = document.getElementsByName("NameOfCheckboxes");
selectedCboxes = Array.prototype.slice.call(checkboxes).filter(ch => ch.checked==true);

Here the Array.prototype.slice.call() part converts the object NodeList of all the checkboxes holding that name ("NameOfCheckboxes") into a new array, on which you then use the filter method. You can then also, for example, extract the values of the checkboxes by adding a .map(ch => ch.value) on the end of line 2. The => is javascript's arrow function notation.

Get all the checked checkbox value in an array - one liner

const data = [...document.querySelectorAll('.inp:checked')].map(e => e.value);
console.log(data);

<div class="row">
    <input class="custom-control-input inp"type="checkbox" id="inlineCheckbox1" Checked value="option1"> 
    <label class="custom-control-label" for="inlineCheckbox1">Option1</label>
    <input class="custom-control-input inp"  type="checkbox" id="inlineCheckbox1" value="option2"> 
    <label class="custom-control-label" for="inlineCheckbox1">Option2</label>
    <input class="custom-control-input inp" Checked  type="checkbox" id="inlineCheckbox1" value="option3"> 
    <label class="custom-control-label" for="inlineCheckbox1">Option3</label>
</div>