Node.js通过if和async调用控制流程

Question

I am porting rails code to node.js and stuck with a control flow problem. What should be the best way to port below code:

filter = {blah:blah};

result = {};

if(filters.something) {
   asyncDBCall(function(){
       result.something = somevalue;
   });
}

if(filters.someOtherThing) {
   asyncDBCall(function() {
       result.someOtherThing = someothervalue;
   });
}

return result;

Answer 1

The major advantage and disadvantage of node JS is it's asynchronous nature while executing functions. Your code should be

if (filters.something) {
    asyncDBCall(function() {
        result.something = somevalue;
        return result;
    });
}

if (filters.someOtherThing) {
    asyncDBCall(function() {
        result.someOtherThing = somevalue;
        return result;
    });
}

However if it is possible that both the conditions are true. In that case you have to wait for the other asyncDBCall to finish before making the next asyncDBCall. The code would be

if (filters.something) {
    asyncDBCall(function() {
        result.something = somevalue;
        if (filters.someOtherThing) {
            asyncDBCall(function() {
                result.someOtherThing = somevalue;
                return result;
            });
        }
    });
}

There is another solution which allows both requests to be sent simultaneously.

var someFlag = false, someOtherFlag = false;
if (filters.something) {
    asyncDBCall(function() {
        result.something = somevalue;
        someFlag = true;
        if (someFlag && someOtherFlag)
            return result;
    });
}

if (filters.someOtherThing) {
    asyncDBCall(function() {
        result.someOtherThing = somevalue;
        someOtherFlag = true;
        if (someFlag && someOtherFlag)
            return result;
    });
}

If you have many properties in filter object, you need to use recursion.

Answer 2

Use async module. Async.parallel will execute the two queries in parallel. Use async.series to execute one after another.

Answer 3

You should consider using JavaScript promises. When you use them, you'll not have to deal with the callback hell which node.js drives you into.