Sorting function not working

In this table sorting function is not working for mail room date,the icon is showing but its not functioning.

This is the code..

<th class="slds-is-sortable" scope="col">
                    <div class="slds-truncate">
                        Document Code
                        <button class="slds-button slds-button--icon-bare">
                            <svg aria-hidden="true"
                                class="slds-button__icon slds-button__icon--small"> <use
                                xlink:href="{!URLFOR($Resource.SLDS0102, 'assets/icons/utility-sprite/svg/symbols.svg#arrowdown')}"></use>
                            </svg>
                            <span class="slds-assistive-text">Sort</span>
                        </button>
                    </div></th>