use jQuery to get values of selected checkboxes

$("#locationthemes").prop("checked")

In jQuery just use an attribute selector like

$('input[name="locationthemes"]:checked');

to select all checked inputs with name "locationthemes"

console.log($('input[name="locationthemes"]:checked').serialize());

//or

$('input[name="locationthemes"]:checked').each(function() {
   console.log(this.value);
});

Demo

---

In VanillaJS

[].forEach.call(document.querySelectorAll('input[name="locationthemes"]:checked'), function(cb) {
   console.log(cb.value); 
});

Demo

---

In ES6/spread operator

[...document.querySelectorAll('input[name="locationthemes"]:checked')]
   .forEach((cb) => console.log(cb.value));

Demo

$('input:checkbox[name=locationthemes]:checked').each(function() 
{
   // add $(this).val() to your array
});

Working Demo

OR

Use jQuery's is() function:

$('input:checkbox[name=locationthemes]').each(function() 
{    
    if($(this).is(':checked'))
      alert($(this).val());
});

​

Map the array is the quickest and cleanest.

var array = $.map($('input[name="locationthemes"]:checked'), function(c){return c.value; })

will return values as an array like:

array => [2,3]

assuming castle and barn were checked and the others were not.