To retrieve the value (true or false) of a checkbox, simply append ".checked" to the checkbox object. For example, if our checkbox has an id="checkBox":
checkBox.checked // will return true or false.
If you need to set the checked attribute to true:
checkBox.checked = true;
It appears that you are using querySelector in your code based on the link provided in the comment. Remember that unlike jQuery, there is no built-in method like "each" for the array-like list returned by querySelectorAll...
When condensed into one line, it can get messy...
To retrieve values:
Array.prototype.forEach.call(document.querySelectorAll('input[type="checkbox"]'), function(checkbox){return checkbox.checked; });
To set values:
Array.prototype.forEach.call(document.querySelectorAll('input[type="checkbox"]'), function(checkbox){checkbox.checked = true; });
edit: Added a "return" keyword to the "get" version.
edit2: Here's a jsfiddle link for reference: http://jsfiddle.net/snlacks/pLgjx4xa/