Question

I would like to return x || $.get.

Or in other words, if x is true, then return x, else perform a GET call and return the value provided by the server.

My attempt is listed below (ideally, it would follow the return x || y format maybe with an anonymous function? instead of the if/then).

Problem is my return from my $.get function appears not to be what I expected.

Would appreciate an explanation of what is going on.

Thanks

$(function(){

  function test(x,y) {
    if(x==true) {return true;}
    else{
      //test.php is echo($_GET['y']==123);
      $.get('ajax.php',{'y':y},function (status) {return status;});
    }
  }

  alert(test(false,123));

});

Answer 1

If you’re using jQuery 1.5 or later, Deferred and Promise are your friend for this kind of thing. Any time you call AJAX calls what you get back are Promise objects which you can attach functions to via .done(), .fail(), and .then().

However! As pointed out by this excellent intro to deferred/promise and all this stuff (http://www.erichynds.com/jquery/using-deferreds-in-jquery/), you can also use $.wait()’s ability to handle a value that isn’t a promise to automatically do caching. So code like this:

$.when(getToken()).done(
  function (token) {
    // do something with the token, which may or may not have been 
    // retrieved from the remote service
  }
);

Can handle getting either a cached value back or a promise with no problem:

function getToken() {
  // Return either the cached value or a jQuery Promise. If $.when() gets the
  // cached value it will immediately realize that you didn't give it a
  // promise and it will instead create a jQuery Deferred to return and
  // .resolve() it using the value it did get. Thus, either way what
  // comes out of the function is something .when() can deal with and call a function.
  if (this.cache["token"]) {
    return this.cache["token"];
  } else {
    return $.get(" ... some url ... ");
  }
};