CoffeeScript:: I can't understand why the function body returns when using ajax

Question

CoffeeScript:: I can't understand why the function body returns when using ajax

Hey there, I'm new to Coffeescript and have a question regarding Ajax.

jQuery ->
  api = 
    getId: ->
      res  = []
      $.ajax
        dataType: "jsonp"
        url: "http://localhost:3004/videos.json"
        success: (data) =>
          if data
            data.forEach (elem) =>
              embed_id = elem.video_id
              res.push(embed_id)
            console.log res
            return res

I tried running this code, and then

console.log res

The output I get is

["id1","id2","id3",...] .

I am hoping that api.getId() would return ["id1","id2","id3",...] However, what I see instead is

Object 
  -> abort
    function(a) {...}
  ...
  -> status: 200
  ...
  -> success: function (){...}

appearing in my debug window.

I really want to retrieve the value of the response.

javascript ajax coffeescript

Answer 1

Answer №1

Understanding asynchronous requests is crucial in JavaScript development, including with Coffeescript. When making XHR calls, it's important to remember that you cannot simply return the result immediately. Instead, you must define a callback function that will handle the response once the call is complete.

It's helpful to inspect the compiled JavaScript code to see how your Coffeescript translates.

getId: ->
   ## .. snip ..
   $.ajax ## .. snip ..

In your code snippet, the getId function returns the XHR object from $.ajax, not the result of the success callback as one might expect. This XHR object can be used for various purposes like monitoring progress, cancelling the request, or modifying additional options.

success: (data) =>
      ## .. snip ..
      return res

Returning a value from an XHR success callback serves little purpose. It's more effective to work with the retrieved data directly within the callback, such as updating the DOM or triggering another function to process the information.

Answer 2

Understanding asynchronous requests is crucial in JavaScript development, including with Coffeescript. When making XHR calls, it's important to remember that you cannot simply return the result immediately. Instead, you must define a callback function that will handle the response once the call is complete.

It's helpful to inspect the compiled JavaScript code to see how your Coffeescript translates.

getId: ->
   ## .. snip ..
   $.ajax ## .. snip ..

In your code snippet, the getId function returns the XHR object from $.ajax, not the result of the success callback as one might expect. This XHR object can be used for various purposes like monitoring progress, cancelling the request, or modifying additional options.

success: (data) =>
      ## .. snip ..
      return res

Returning a value from an XHR success callback serves little purpose. It's more effective to work with the retrieved data directly within the callback, such as updating the DOM or triggering another function to process the information.

Answer 3

Answer №2

The statement return res is located within an AJAX call. It does not actually return from the getId() function, but rather from the inner AJAX callback. This approach will not work as intended. Since AJAX calls are asynchronous, you cannot force them to be synchronous. I recommend structuring your code like this instead:

jQuery ->
  api = 
    getId: (callback) ->
      res  = []
      $.ajax
        dataType: "jsonp"
        url: "http://localhost:3004/videos.json"
        success: (data) =>
          if data
            data.forEach (elem) =>
              embed_id = elem.video_id
              res.push(embed_id)
            callback(res)
          else
            callback(null)
        error: =>
          callback(null)

Then in your code, you can utilize it like this:

api.getId(function(res) {
  // do something with the result.
});
// execute other tasks...

Remember that the code labeled as execute other tasks... may be executed before the code handling do something with the result.

Apologies for mixing CoffeeScript with JavaScript; I am more comfortable with plain JavaScript.

Answer 4

The statement return res is located within an AJAX call. It does not actually return from the getId() function, but rather from the inner AJAX callback. This approach will not work as intended. Since AJAX calls are asynchronous, you cannot force them to be synchronous. I recommend structuring your code like this instead:

jQuery ->
  api = 
    getId: (callback) ->
      res  = []
      $.ajax
        dataType: "jsonp"
        url: "http://localhost:3004/videos.json"
        success: (data) =>
          if data
            data.forEach (elem) =>
              embed_id = elem.video_id
              res.push(embed_id)
            callback(res)
          else
            callback(null)
        error: =>
          callback(null)

Then in your code, you can utilize it like this:

api.getId(function(res) {
  // do something with the result.
});
// execute other tasks...

Remember that the code labeled as execute other tasks... may be executed before the code handling do something with the result.

Apologies for mixing CoffeeScript with JavaScript; I am more comfortable with plain JavaScript.

CoffeeScript:: I can't understand why the function body returns when using ajax

Answer №1

Answer №2

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