Question

I have a very limited knowledge about node and nob-blocking IO so forgive me if my question is too naive.

In order to return needed information in response body, I need to

• Make a call to 3rd party API
• Wait for response
• Add some modifications and return JSON response with the information I got from API.

My question is.. how can I wait for response? Or is it possible to send the information to the client only when I received response from API (as far as I know, connection should be bidirectional in this case which means I won’t be able to do so using HTTP).

And yet another question. If one request waits for response from API, does this mean than other users will be forced to wait too (since node is single-threaded) until I increase numbers of threads/processes from 1 to N?

Answer 1

You pass a callback to the function which calls the service. If the service is a database, for example:

db.connect(host, callback);

And somewhere else in the code:

var callback = function(err, dbObject) {
    // The connection was made, it's safe to handle the code here
    console.log(dbObject.status);
    res.json(jsonObject, 200)
};

Or you can use anonymous functions, so:

db.connect(host, function(err, dbObject) {
    // The connection was made, it's safe to handle the code here
    console.log(dbObject.status);
    res.json(jsonObject, 200)
});

Between the call and the callback, node handles other clients / connections freely, “non-blocking”.