JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" name="userpages[]" id="1" value="1"/>
<input type="checkbox" name="userpages[]" id="2" value="2"/>
<input type="checkbox" name="userpages[]" id="3" value="3"/>
<input type="checkbox" name="userpages[]" id="4" value="4"/>

JavaScript

var data = []

$('input[name="userpages[]"').each (function (index, element) {
    data[$(element).attr('id')] = $(element).val();
});
console.log(data);