Parallel function calls in Node.js

Question

I need to do a few independent database queries in Node.js. After all queries are executed, response should be sent. My first try looks like this:

templateDa         


        

Answer 1

You could just use a function that checks if all the data is present as your callback to your queries, and if all the data is present then the response could be sent. So something like

function checkData(){
    if (templateData.A && templateData.B && templateData.C){
        //send your response
    }
}

then just don't nest your calls

model.getA(function(result){
    templateData.A = result;
    checkData();
}

model.getB(function(result){
    templateData.B = result;
    checkData();
}

model.getC(function(result){
    templateData.C = result;
    checkData();
}

When all three have completed your response will be sent.

Answer 2

Use the async package: (npm install async)

async.parallel([
    function(){ ... },
    function(){ ... }
], callback);

https://github.com/caolan/async#parallel

Alternatively, you can use promises:

Q.spread(
    [ model.getA(), model.getB(), model.getC() ],
    function(a, b, c) {
        // set templateData
        return templateData;
    }
).then(...);

(assuming that the get*() methods return promises)