[clug] javascript jquery and long calls

[Neill Cox]

First let me admit that I don't really understand JavaScript's scoping rules
or closures, but until someone who know what they are talking about comes
along...

I think what's tripping you up is that in JavaScript functions are objects.
 bar and setup are different objects and therefore "this" (which in
JavaScript is a keyword rather than an identifier) in each function resolves
to that function, meaning that they each have their own this.url,
this.waitForMessage etc.

x = function () { this.b = 'fred'; return this.b }
 function () { this.b = 'fred'; return this.b }
 y = function () { this.b = 'george'; return this.b }
 function () { this.b = 'george'; return this.b }
 z = { f_x:x, f_y:y }
  Object
z.f_x
 function () { this.b = 'fred'; return this.b }
 z.f_x()
 "fred"
 z.f_y()
 "george"

If you want to share information between them you will need to either pass
parameters or declare a global (or a variable in the enclosing scope)

Perhaps:

var bar = {
  url:"",
  textout:"",
  setup: function(p_url, p_textout) {
    url=p_url;
    textout=p_textout;
    waitForMessage();
  },
  waitForMessage: function() { ...}
}

or

function bar() {
  var url;
  var textout;

  function setup(p_url, p_textout) {
    url = p_url;
    textout = p_textout;
    waitForMessage();
  }

  function waitForMessage() {
   ...
  }
}

This form begs the question of how you will get p_url and p_textout to the
setup function though. I guess bar.setup('http://example.com/gettext',
myArray) might work, but it looks odd.

Also is there a reason you are not setting the timeout using the option of
the jQuery Ajax object?

I have a feeling looking at this that either I don't understand what you are
up to, or there is likely to be a simpler way than what I have suggested.

Cheers,
Neill


On Wed, Mar 30, 2011 at 4:35 PM, jm <jeffm at ghostgun.com> wrote:

> I'm experimenting with comet a  the moment using jquery. The problem I'm
> having is the variable 'this' doesn't appear to be in scope. What I'm
> trying to do in set up an object which stores various bits of information,
> eg this.url should be the URL to call and this.textout should be the div to
> write the messages to, this object has the method waitForMessage() as
> defined below. The expected behaviour is that I call it once, makes a call
> to the remote url, then falls through while waiting due to async being true,
> it then appends the returned text to the div, and calls itself.
>
> function bar() {
>    this.setup = setup;
>    this.waitForMessage = waitForMessage;
> }
>
> function setup(url, textout) {
>  this.url = url;
>  this.textout = textout;
>  this.waitForMessage();
> }
>
> function waitForMessage() {
>    $.ajax({
>            url: this.url,
>                async: true,
>                cache: false,
>                success: function(data){
>                if (data.text) {
>                    for(var i = 0; i < data.text.length; i++) {
>                        this.textout.append($(data.text[i]));
>                    }
>                }
>                setTimeout('waitForMessage()', 1000);
>            }
>        });
> }
>
> Can anyone tell me how this SHOULD be written?
>
>
> Jeff.
>
>
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