<a href="javascript:if(ConfirmChoice('Delete row?', 'Are you sure you want to delete this row?')) DeleteRow('{!imported.Id}');" style="font-weight:bold">Delete</a>

function ConfirmChoice(title, message) {

        ConfirmDialog(title, message).then(function(answer) {
            return answer;
        });
    }

    function ConfirmDialog(title, message) {
        var defer = $.Deferred();
        var yesButton = document.getElementById('yes');
        var noButton = document.getElementById('no');
        var confirmationDialog = document.getElementById('confirmationDialog');

        document.getElementById('confirmationTitle').innerHTML = title;
        document.getElementById('confirmationMessage').innerHTML = message;
        confirmationDialog.showModal();

        // Update button opens a modal dialog
        yesButton.addEventListener('click', function() {
            defer.resolve("true");
            confirmationDialog.close();
        });

        // Form cancel button closes the dialog box
        noButton.addEventListener('click', function() {
            defer.resolve("false");
            confirmationDialog.close();
        });

        return defer.promise();
    }

<a href="javascript:if(window.confirm('Are you sure you want to delete this row?')) DeleteRow('{!imported.Id}');" style="font-weight:bold">Delete</a>