JavaScript 'await' throws error 'then is not defined'

Question

JavaScript 'await' throws error 'then is not defined'

Just starting out with async programming and I've noticed a common issue in similar threads - the problem of not returning anything. However, in my case, I am facing a different error message 'Cannot read property 'then' of undefined'.

function getWorkItems(iterationPath, projectId) {

    var queryClient = VSS_Service.getCollectionClient(TFS_Wit_QueryAPI.WorkItemTrackingHttpClient);
    var query = { query: "SELECT [System.Id] FROM WorkItem WHERE [System.IterationPath] = '" + iterationPath + "'" };
    var resultOfQuery;

    queryClient.queryByWiql(query, projectId).then(

        function (resultOfQuery) {
            return new Promise((resolve, reject) => {
                resolve(resultOfQuery);
                console.log("Debug: " + JSON.stringify(resultOfQuery));
            })
            VSS.notifyLoadSucceeded();

        });
}

Although the debug message is printed successfully and data is fetched from the server, an error occurs when calling it from another location.

let bar;

getWorkItems(counter.path, projectId).then ( res => {
    bar = res;
    console.log("Debug: should be output of query " + JSON.stringify(bar));
})

The error message 'Cannot read property 'then' of undefined' pops up in this scenario.

javascript ajax

Answer 1

Answer №1

When looking at the code for getWorkItems, it's important to note that there is no explicit return statement, which means it will implicitly return undefined. Additionally, as

queryClient.queryByWiql(query, projectId)

is already returning a promise, there is no need to create another promise. You can simply streamline the function like this:

function retrieveWorkItems(iterationPath, projectId)
{
  var queryClient = VSS_Service.getCollectionClient(TFS_Wit_QueryAPI.WorkItemTrackingHttpClient);
  var query = { query: "SELECT [System.Id] FROM WorkItem WHERE [System.IterationPath] = '" + iterationPath + "'" };
  return queryClient.queryByWiql(query, projectId);
}

If you wish to include a log statement and notifyLoadSucceeded within the function, you can do so without creating an additional promise. When inside a .then callback, you just need to return the desired value for the promise resolution:

function retrieveWorkItems(iterationPath, projectId)
{
  var queryClient = VSS_Service.getCollectionClient(TFS_Wit_QueryAPI.WorkItemTrackingHttpClient);
  var query = { query: "SELECT [System.Id] FROM WorkItem WHERE [System.IterationPath] = '" + iterationPath + "'" };
  return queryClient.queryByWiql(query, projectId)
    .then(function(queryResult) {
      console.log("Debug: " + JSON.stringify(queryResult));
      VSS.notifyLoadSucceeded();
      return queryResult;
    });
}

Answer 2

When looking at the code for getWorkItems, it's important to note that there is no explicit return statement, which means it will implicitly return undefined. Additionally, as

queryClient.queryByWiql(query, projectId)

is already returning a promise, there is no need to create another promise. You can simply streamline the function like this:

function retrieveWorkItems(iterationPath, projectId)
{
  var queryClient = VSS_Service.getCollectionClient(TFS_Wit_QueryAPI.WorkItemTrackingHttpClient);
  var query = { query: "SELECT [System.Id] FROM WorkItem WHERE [System.IterationPath] = '" + iterationPath + "'" };
  return queryClient.queryByWiql(query, projectId);
}

If you wish to include a log statement and notifyLoadSucceeded within the function, you can do so without creating an additional promise. When inside a .then callback, you just need to return the desired value for the promise resolution:

function retrieveWorkItems(iterationPath, projectId)
{
  var queryClient = VSS_Service.getCollectionClient(TFS_Wit_QueryAPI.WorkItemTrackingHttpClient);
  var query = { query: "SELECT [System.Id] FROM WorkItem WHERE [System.IterationPath] = '" + iterationPath + "'" };
  return queryClient.queryByWiql(query, projectId)
    .then(function(queryResult) {
      console.log("Debug: " + JSON.stringify(queryResult));
      VSS.notifyLoadSucceeded();
      return queryResult;
    });
}

JavaScript 'await' throws error 'then is not defined'

Answer №1

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