JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" class="mycheck" />
<input type="checkbox" class="mycheck" />
<input type="checkbox" class="mycheck" />
<input type="checkbox" class="mycheck" />
<input type="checkbox" class="mycheck" />

JavaScript

var checkboxes = $('.mycheck');
for(var i=0;i<5;i++) {  //normally would use each, but acting like the OP code
    var checkbox = checkboxes.eq(i);
    checkbox.prop('checked',true); //should work
    console.log(i, checkbox.prop('checked'));
}