CODEWITHSUNDEEP
javascriptmongodbcallbackmapreduce
Tiago Espinha
Tiago Espinha

Reputation: 1209

Map/Reduce example... is this correct?

More than once have I seen the following reduce function as a mapreduce usage example for mongodb:

function reduce(key, values) {
    var result = {count:0};
    values.forEach(function(value) {
        result.count += value.count;
    });
    return result;
}

But this strikes me as very odd. The iterating is done with the .forEach() method which uses a callback function to do the counting. However, we return result; right away.

Can't it be the case sometimes that we return the result variable before the callback is done iterating through the values?

I thought the purpose of callbacks is that we delegate it to a (possibly) different thread while the main control flow continues normally.

Upvotes: 0

Views: 382

Answers (1)

Cerbrus
Cerbrus

Reputation: 72967

forEach isn't asynchronous.
The return statement will only be executed after the forEach is done.

Upvotes: 3

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