notify Q Promise progress in Node.js

Question

I wanted to use Q Promise Progress functionality, I have this code and i want to catch progress and when progress is 100, then resolve the Promise :

var q = require("q");

var a =  function(){
    return q.Promise(function(resolve, reject, notify){
        var percentage = 0;
        var interval = setInterval(function() {
            percentage += 20;
            notify(percentage);
            if (percentage === 100) {
                resolve("a");
                clearInterval(interval);
            }
        }, 500);
    });
};

var master = a();

master.then(function(res) {
    console.log(res);
})

.then(function(progress){
    console.log(progress);
});

But i get this error:

Error: Estimate values should be a number of miliseconds in the future

Why?

Answer 1

I don't get this error, if i try to run your script (node 4.2.1), but you never listen to the progress of the promise. You need to register the progressHandler as third parameter to the .then function:

var q = require("q");

var a =  function(){
    return q.Promise(function(resolve, reject, notify){
        var percentage = 0;
        var interval = setInterval(function() {
            percentage += 20;                
            notify(percentage);
            if (percentage === 100) {
                resolve("a");
                clearInterval(interval);
           }
        }, 500);
    });
};

function errorHandler(err) {
  console.log('Error Handler:', err);
}

var master = a();

master.then(function(res) {
    console.log(res);
}, 
errorHandler,
function(progress){
    console.log(progress);
});

Output:

20
40
60
80
100
a

You must register the progress callback as third parameter to the .then -function or you can use the special .progress() shorthand, see https://github.com/kriskowal/q#progress-notification

Here is the call chain with the progress shorthand:

var master = a();
master.progress(function(progress{
    console.log(progress)})
.then(function(res) {
    console.log(res);
});

In your code, console.log(progress) prints undefined , because the function is listen to the result of the previous .then -statement, which returns nothing.