How to use promise in constructor?

[Louis Sherren]

I have to do some async call in some constructor, like retrieve data from mysql. 

I'm trying to use Promise to handle the 'async' thing but I find it impossible because:

I must return Promise object in constructor but the constructor is called by 'new' key word, there shouldn't be any 'return' in constructor.

Is there some way to do this piece of work?

Now I just add another function like 'init' to do the async part, can I do it in constructor ?

[Aria Stewart]

There's two things you can do: use a plain function and call your constructor internally:

function createThing(args) {
return doPrep.then(function (prepdata) { return new Thing(prepdata, args); })
}

Or do the prep work in the constructor, but have the object not fully ready to use -- which if you think of promises as future values and not flow control, makes perfect sense:

function Thing(args) {
this.prep = doPrep();
}

/* Later */
var thing = new Thing();
thing.prep.then(function (prepdata) { ... })

What is the actual task you're trying to accomplish?

Aria

[Axel Kittenberger]

Just wrap it in a "factory". I usually call it whatever.create().

Then use with it whatever flow control thingy you prefer. callbacks, generator/suspend, etc.

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