Question

How do I get the value of the text from the example below?

Q.js has an example on using Deferred:

var deferred = Q.defer();
FS.readFile("foo.txt", "utf-8", function (error, text) {
    if (error) {
        deferred.reject(new Error(error));
    } else {
        deferred.resolve(text);
    }
});
return deferred.promise;

In this case, there is a node async function being used. What I want to do is get the value of text from the deferred.promise being returned. When I console.log(deferred.promise) I get this:

{ promiseSend: [Function], valueOf: [Function] }

What am I doing wrong (as I just copy/pasted the example from here: https://github.com/kriskowal/q#using-deferreds) or what else do I need to do to actually get that text from the file?

I am aware that node.js has a synchronous version of the call above – my goal is to understand how deferred works with this library.

Answer 1

You can get the value via the .then() method of a Promise:

function read() {
    // your snippet here...
}

read().then(function (text) {
    console.log(text);
});

Also, error handlers can be passed either as a 2nd argument to .then() or with the .fail() method:

read().fail(function (err) {
    console.log(err);
});