Deferred.when/dojo.when

since:V1.5

Contents

• Deferred.when/dojo.when
  • Usage
  • See Also

dojo.when provides the ability to define a callback (and error handler) for the eventual completion of a Deferred or promise object, or any standard synchronous value.

As of Dojo 1.7, the when function is exposed as a member of the dojo/_base/Deferred module return (which is also the Deferred constructor). It is aliased to dojo.when for backward-compatibility.

Usage

The first argument to dojo.when may be any value, the second argument is the callback, and the optional third argument is the error callback. If the first argument is a promise (like a Deferred object), then the callback (or error callback) will be called when the promise is resolved. If the first argument is not a promise, the callback will be call immediately (with the value passed as the first argument.

Example 1: Creating and calling a deferred (1.7+ AMD).

require(["dojo/_base/Deferred"], function(Deferred){

  Deferred.when(4, print); // this will print 4 immediately

  var fourAsync = new Deferred();
  Deferred.when(fourAsync, print); // this will print 4, one second later when the Deferred is resolved
  setTimeout(function(){
    fourAsync.resolve(4);
  }, 1000);

  function print(value){
    console.log(value);
  };
});

require(["dojo/_base/Deferred"], function(Deferred){ Deferred.when(4, print); // this will print 4 immediately var fourAsync = new Deferred(); Deferred.when(fourAsync, print); // this will print 4, one second later when the Deferred is resolved setTimeout(function(){ fourAsync.resolve(4); }, 1000); function print(value){ console.log(value); }; });

Example 2: Creating and calling a deferred (Dojo < 1.7 style).

dojo.when(4, print); // this will print 4 immediately

var fourAsync = new dojo.Deferred();
dojo.when(fourAsync, print); // this will print 4, one second later when the Deferred is resolved
setTimeout(function(){
  fourAsync.resolve(4);
}, 1000);

function print(value){
  console.log(value);
}

dojo.when(4, print); // this will print 4 immediately var fourAsync = new dojo.Deferred(); dojo.when(fourAsync, print); // this will print 4, one second later when the Deferred is resolved setTimeout(function(){ fourAsync.resolve(4); }, 1000); function print(value){ console.log(value); }

See Also

• dojo.Deferred()
• Article on the new design of Deferreds in 1.5: http://www.sitepen.com/blog/2010/05/03/robust-promises-with-dojo-deferred-1-5/

Table of Contents

• Deferred.when/dojo.when
  • Usage
    • Example 1: Creating and calling a deferred (1.7+ AMD).
    • Example 2: Creating and calling a deferred (Dojo < 1.7 style).
  • See Also