JSFiddle - React, Tailwind, and code Playground

by scaillerie

HTML

<select name="weekId" id="weekId" onchange="getSelected(value)">
   <option value="Select">Select</option>
   <option value="Weekly">Weekly</option>
   <option value="Monthly">Monthly</option>
   <option value="Both">Both</option>
</select>


<select id="selectedWeek" name="selectedWeek" size="5" multiple="multiple"/>

JavaScript

function getSelected(value) {
    var selectedWeek = document.getElementById("selectedWeek"),
        nbOptions = selectedWeek.length;

    // Don't add the value if already present
    for (var i = 0; i < nbOptions; i++) {
        if(selectedWeek.options[i].value === value) return;
    };

    // If not found add it
    selectedWeek.innerHTML += '<option value="' + value + '">' + value + '</option>';
}