How to make an ASP.NET field required via javascript

<div class="row commentType">
        <div class="form-group col col-lg-3">
            <br/>
            <label>Select comment type</label>
            <br />
            <br />
            <select class="form-control bg-secondary text-light " aria-label="Default select example" name="selectcommentType" onchange="handleSelectChange(event)">
                <option value="1">Generic</option>
                <option value="2">Account Details</option>
                <option value="3">Order</option>
                <option value="4">Shipping details/option>
                <option value="5">other</option>

            </select>
        </div>
    </div>
<div class="row" id="ChangePassword" style="display:none;">
        <br />
        <br />
        <div class="form-group col col-lg-3">
            <label>Method for Password Change</label>
            <br />
            <br />
        </div>
        <div class="form-check">
            <input class="form-check-input" type="radio" name="changePasswordMethod" id="changePasswordMethod2" onclick="passwordChangeMethod(2)" checked>
            <label class="form-check-label" for="changePasswordMethod2">
                By email
            </label>
        </div>
        <div class="form-check">
            <input class="form-check-input" type="radio" name="changePasswordMethod" id="changePasswordMethod1" onclick="passwordChangeMethod(1)">
            <label class="form-check-label" for="changePasswordMethod1">
                By post
            </label>
        </div>
        <br />
        <br />
    </div>

<div class="row" id="ChangePasswordViaEmail" style="display:none;">
        <br />
        <br />
        <div class="form-group col col-lg-3">
            <label>Email for password change</label> @Html.TextBoxFor(model => model.newEmail, new { htmlAttributes = new { @class = "form-control", @placeholder = "Enter respondent's email here...", @type = "email", id = "Email1"} })
        </div>
        <br />
        <br />
    </div>

<script>
 function handleSelectChange(event) {

            var selectElement = event.target;
            var value = selectElement.value;
            if (value == 2) {
                document.getElementById('ChangePassword').style.display = 'block';

                document.getElementById('ChangePasswordViaEmail').style.display = 'block';
                document.getElementById('ChangePasswordViaPost').style.display = 'none';

            }
            }


        function passwordChangeMethod(val) {

            if (val == 1) {
                document.getElementById('ChangePasswordViaEmail').style.display = 'none';
                document.getElementById('ChangePasswordViaPost').style.display = "block";
            }
            else if (val == 2) {
                document.getElementById('ChangePasswordViaPost').style.display = 'none';
                document.getElementById('ChangePasswordViaEmail').style.display = 'block';
                document.getElementById('Email1').required = "required";
            }

    </script>