AsyncResult.status property (apps for Office)

function getData() {
    Office.context.document.getSelectedDataAsync(Office.CoercionType.Table, function(asyncResult) {
        if (asyncResult.status == Office.AsyncResultStatus.Failed) {
            write(asyncResult.error.message);
        }
        else {
            write(asyncResult.value);
        }
    });
}
// Function that writes to a div with id='message' on the page.
function write(message){
    document.getElementById('message').innerText += message; 
}