function openDialog(listId) {
SP.SOD.executeOrDelayUntilScriptLoaded(function () {
    SP.UI.ModalDialog.showModalDialog({
        url: 'http://yoursite/yourweb/_layouts/15/listform.aspx?PageType=8&ListID={' + listId + '}&IsDlg=1',
        title: 'New Item',
        allowMaximize: false,
        showClose: true,
        width: 500,
        height: 300,
        dialogReturnValueCallback: function(dialogResult, returnValue) {
            SP.UI.ModalDialog.RefreshPage(SP.UI.DialogResult.OK);
        }
    });
}, 'sp.ui.dialog.js');
}

<a href="javascript:..."></a>