The length of the HTTP response in Angular is not defined

Currently, I am utilizing Angular in conjunction with jQuery Mobile to develop multiple pages, but I have encountered an obstacle when using the $http service to connect to my JSON requests. While populating a few arrays with functions and successfully retrieving data for my pages, I am occasionally facing errors such as:

Cannot read property 'length' of undefined

The snippet of my code contributing to this issue is as follows:

$http.jsonp(url).success(function(data) {
  for (i=0; i<data.PROJECT.length; i++)
      $scope.ProjectList.push( { id:data.PROJECT[i].PROJECT_CODE, name:data.PROJECT[i].PROJECT_DESC } );
});

The problem seems to arise within the 'For' loop section of my code. I attempted an alternative approach using "then", which looks like this:

var request = $http.jsonp(url);
return request.then(function(request) { return request.data.PROJECT; }, handleError );

Despite implementing this change, the same error persists, or sometimes there are no errors with blank results. Could anyone help identify what I might be doing incorrectly? Each API call has its own function, so object reusability should not be an issue (though there may be concerns about appending objects). Additionally, after separating my code into controller/service - part 2 of the project - I continue experiencing these errors.

UPDATE

To further illustrate the intermittent nature of this issue, I have set up a jsFiddle demo available here. Upon running the demonstration multiple times, you will observe that the arrays intermittently return empty values. If console logs were accessible, you would notice that ProjectList contains the resultset of EquipList at times, and vice versa.

Answer №1

Unfortunately, I am unable to comment on SO yet, so I will provide my response here. Based on your

... with the exception of sometimes encountering errors like this

it appears that the URL you are trying to access is not functioning correctly. Assuming that your JSON response follows this structure:

{
  "PROJECT": [ 
    { "PROJECT_CODE": ..., "PROJECT_DESC": ... },
    ...
  ]
}

If you are experiencing intermittent issues, it is likely that the server is returning a response different from the expected structure mentioned above, while still indicating a HTTP status 200 OK.

I recommend monitoring your network requests to analyze the actual response, or adding a console.log of data within the success function.

--- EDIT

Upon further investigation, it seems to be primarily an API-related problem. The API appears to occasionally return the correct list(s), but more often than not (at least for now) it returns a HTTP 200 OK without any data (Content-Length: 0). Since your fiddle does not clearly indicate when it's loading, I made some adjustments to your code here: http://jsfiddle.net/gce4ns9a/15/. The reason why you never see 'This never shows up' is because the API responds with 'OK' instead of an error code such as HTTP 500 Internal Server Error or something similar.

I hope this information proves useful to you.

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