JSFiddle - React, Tailwind, and code Playground

HTML

<div class="row-fluid" id="set_alarm">
    <label class="checkbox inline"><input type="checkbox" id="select_all"><b>Select All</b></label><br>
    <label class="checkbox inline days"><input type="checkbox" id="Mon"><b>Mon</b></label>
    <label class="checkbox inline days"><input type="checkbox" id="Tue"><b>Tue</b></label>

</div>

JavaScript

$('#select_all').change(function() {
        $('.days input[type="checkbox"]').attr("checked", this.checked);
  
});