[html5] Waiting for an object to be defined in javascript

[Larry Martell]

On Thu, May 22, 2014 at 3:59 PM, Bill Barron <bill.r.barron at gmail.com> wrote:
> Think of it this way. It is this mailing list's responsibility to send email
> updates to its subscribers as they come in and not the subscribers
> responsibility to check for updates every 10 seconds. This is not only less
> resource intensive for the mailing list, it's also more efficient for the
> subscribers.

Thanks I appreciate your replies. I understand about event driven
programming vs polling. This is a big nasty old PHP app that I
inherited. I was asked to add client side column based sorting to it,
which I did using the sorttable package
(http://www.kryogenix.org/code/browser/sorttable/). That was all fine.
Then I was asked to make the client side sort selection persist across
a server side refresh. This is where I went down the rabbit hole. To
achieve this I added a hidden field that gets set to the sort column
id (along with the sort direction) by the sorttable onclick handler. I
pass that back with the form to the server, who passes it back to the
browser. I then test for it, and if it's set I call the sorttable
function. Problem is that I can't call the function before it is
defined. I think I have this solved with this code:

var interval = setInterval(function() {
    if (typeof(parent.frames['main_frame'].sorttable) === 'undefined') return;
    if (! parent.frames['main_frame'].sorttable.hasOwnProperty('innerSortFunction'))
return;
    clearInterval(interval);
    parent.frames['main_frame'].sorttable.innerSortFunction.apply(parent.frames['main_frame'].document.getElementById("OpenFace-3"),
[]);
}

It may not be pretty, but it appear to be working and I can move on to
more interesting things.


> On Thu, May 22, 2014 at 2:49 PM, Bill Barron <bill.r.barron at gmail.com>
> wrote:
>>
>> I agree with Rick. You need to see what code is defining someObject or
>> what code is setting the class on the table and when that code defines
>> someObject it should trigger an event that the rest of your code listens for
>> or provide some method of checking when it has loaded. If this is Modernizr
>> and you're doing feature detection, then check out Modernizr.load().
>> (formerly YepNope). If you are just waiting for a script to load, you may be
>> interested in AMD JavaScript modules.  If your scripts are loaded and you
>> are just waiting for some event to take place or some object to be defined,
>> then modify the code that defines someObject or sets the table class or see
>> if it has functionality built in already to notify the rest of your code
>> that it is ready. It is that object's job to notify the rest of your code
>> through events or promises that it has done it's part and defined
>> someObject.
>>
>> If the thing that defines someObject is your own code and not a 3rd party
>> library or framework, consider adding a getSomeObject method that returns a
>> promise. That way you could just do this:
>>
>> getSomeObject.then(function (someObject) {
>>     // use someObject here
>> });
>>
>> Thanks,
>> Bill
>>
>>
>> On Thu, May 22, 2014 at 2:41 PM, Larry Martell <larry.martell at gmail.com>
>> wrote:
>>>
>>> On Thu, May 22, 2014 at 3:13 PM, Rik Sagar <org.whatwg at sagar.org> wrote:
>>> > Depends where the object comes from is and who's setting it!
>>> >
>>> > Couldn't you fire an event when the object is created, then do whatever
>>> > work
>>> > you need to do in the event listener ?
>>> >
>>> > Alternatively, can "someObject" be an object inside "otherObject", for
>>> > example, otherObject.someObject.
>>> >
>>> > If you have it that way, you can write a setter/getter on "otherObject"
>>> > for
>>> > someObject.  When someone does "otherObject.someObject = new Object();"
>>> > your
>>> > setter function gets called with the new value.
>>> >
>>> > Either is preferable to the busy loop approach if you can do it.
>>>
>>> The scenario is: After my page is loaded I need to call a js function
>>> that will only exist some time after a table gets given a certain
>>> class. When I try to call that function from an onload function it
>>> fails most of the time because the function has not yet been defined.
>>> If I call that function from a setTimeout that waits 1 second it works
>>> 99% of the time. I'd like to just wait until the class gets put on the
>>> table and the function exists and then call it.
>>>
>>> I think I may have this working. I did this:
>>>
>>> var interval = setInterval(function() {
>>>     if (typeof elem == 'undefined') return;
>>>     clearInterval(interval);
>>>
>>>     // the rest of the code
>>> }, 10);
>>>
>>> So far this looks good. I need to run it for a day or 2 and make sure.
>>>
>>>
>>> > On Thu, May 22, 2014 at 10:32 AM, Larry Martell
>>> > <larry.martell at gmail.com>
>>> > wrote:
>>> >>
>>> >> I need to do the equivalent of this in javascript:
>>> >>
>>> >> while (typeof someObject == 'undefined') {
>>> >>      sleep(10);  // 10ms
>>> >> }
>>> >>
>>> >> And I just can't quite figure out how to code this.
>>> >>
>>> >> I have this:
>>> >>
>>> >>
>>> >> function sleep(ms, callback, arg) {
>>> >>     setTimeout(function() {
>>> >>         callback(arg);
>>> >>     }, ms);
>>> >> }
>>> >>
>>> >> function waitForDef(elem) {
>>> >>     if (typeof elem == 'undefined') {
>>> >>         sleep(10, waitForDef, elem)
>>> >>     }
>>> >> }
>>> >>
>>> >> But it's not clear to me how to use this from my code.
>>> _______________________________________________
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>>> Help at lists.whatwg.org
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>>
>>
>