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" class="days" id="Mon"><b>Mon</b></label>
    <label class="checkbox inline days"><input type="checkbox"  class="days" id="Tue"><b>Tue</b></label>

</div>

JavaScript

$('#select_all').change(function() {
 
    
        $('.days').prop("checked", this.checked);
     
});

$('.days').change(function(){

    if($('input:checkbox:checked.days').length === $("input:checkbox.days").length)
    {
        $('#select_all').prop("checked",true);
    }
    else
    {
        $('#select_all').prop("checked",false);
    }

})