How do I add a listener to JavaScript Object variable?

Question

I have an object generated by this code, but I can only use it when its obj.ready property is == true. I can use only pure JavaScript or Prototypejs. It script is inserted as source (< script src=...).

Is there a way to detect when the object is ready to use? I tried to put observer on dom:loaded, but it didn't work.

I use

PagSeguroDirectPayment.setSessionId('someTextHere');
PagSeguroDirectPayment.getSenderHash();

The second line doesnt work because the object is not ready yet.

Any help is appreciated.

Please post the code here. Reduce it to the most relevant part only. — Felix Kling
– Felix Kling, Commented Apr 12, 2014 at 23:03
Hi Felix. The code in the library is not relevant, but I'll add other parts here. — Ricardo Martins
– Ricardo Martins, Commented Apr 12, 2014 at 23:14

c-smile · Accepted Answer · 2014-04-12 23:30:43Z

2

If you have no infrastructure of events there then the only option is to do polling:

function whenReady(obj, callback) {
  var iid = setInterval(function() {
    if(obj.ready) {
      callback();
      clearInterval(iid);
    }
  }, 20);
}

And to use it as:

PagSeguroDirectPayment.setSessionId('someTextHere');
whenReady(PagSeguroDirectPayment, function() {
  PagSeguroDirectPayment.getSenderHash(); 
});

answered Apr 12, 2014 at 23:30

c-smile

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2 Comments

Ricardo Martins Over a year ago

I thought about interval, but I'm afraid that there's a less agressive option. =) But it works. Thank you very much.

c-smile Over a year ago

@RicardoMartins Another approach would be to use Object.observe(callback) so without polling but it a) didn't land into browsers widely and b) not too much less "aggressive" than polling. But I suspect that code you citing has mechanism of events allowing you to subscribe on "ready" event.

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