JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" name="test" />
<input type="checkbox" name="test" />
<input type="checkbox" name="test" />
<input type="checkbox" name="test" />
<input type="checkbox" name="test" />
<input type="checkbox" name="test" />
<input type="checkbox" name="test" />

JavaScript

var elements = document.getElementsByName("test");
for (i = 0, len = elements.length; i < len; i++) {
    elements[i].checked = true;
}