JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" id="c1">
<input type="checkbox" id="c2">
<input type="checkbox" id="c3">

JavaScript

var ids = [],
    cbx = document.querySelectorAll('input[type="checkbox"]');

for (i = 0, l = cbx.length; i < l; i++) {
        ids.push(cbx[i].id);
}

console.log(ids)