How does Angular $q.when work?

Question

Can some one explain me how does $q.when work in AngularJS? I'm trying to analyse how $http work and found this:

var promise = $q.when(config);

And here is config object from Chrome console:

Object {transformRequest: Array[1], transformResponse: Array[1], cache: Object, method: "GET", url: "/schedule/month_index.html"…}
cache: Object
headers: Object
method: "GET"
transformRequest: Array[1]
transformResponse: Array[1]
url: "/schedule/month_index.html"
__proto__: Object

What happens next? How this object get's resolved or rejected?

Solution

Calling $q.when takes a promise or any other type, if it is not a promise then it will wrap it in a promise and call resolve. If you pass a value to it then it is never going to be rejected.

From the docs:

Wraps an object that might be a value or a (3rd party) then-able promise into a $q promise. This is useful when you are dealing with an object that might or might not be a promise, or if the promise comes from a source that can't be trusted.

Comments

[SET001]

If you pass a value to it - but what if I passing object?

[Phrygian Moon]

value, object, array it is all the same.

[Onur Topal]

what if I pass a function that returns a promise? does it mean the then callback of it will be passed the promise result param send by resolve?

[jrista]

Onur, when you say pass a function, do you mean as a function object: $q.when(myfunc), or by invoking the function your passing in: $q.when(myfunc())? I don't know exactly what the former will do...the latter will invoke myfunc() first, and pass the returned promise|value to .when().