use jQuery to get values of selected checkboxes

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

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In VanillaJS

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

Demo

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In ES6/spread operator

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

Demo