CODEWITHSUNDEEP
javascriptnode.jsq
akaphenom
akaphenom

Reputation: 6888

Better way to write this promise chain

I am learning Node and have a function that recurses a directory and returns promise of files that match a pattern. This is working pretty good, but I want to be able to handle files of any number of types simultaneously, and I am chaining the functions like this:

findFiles(scriptLocation, '.type1.').then(function (type1Files) { 
    console.log('type1Files: ' + type1Files) 
    findFiles(scriptLocation, '.type2.').then(function (type2Files) {
        console.log('type2Files: ' + type2Files) 
        findFiles(scriptLocation, '.type3.').then(function (type3Files) {
            console.log('type3Files: ' + type3Files) 
        })
    })
})

But it could get pretty sloppy as I add more types. I tried

Q.all([
    findFiles(scriptLocation, '.type1.')
    , findFiles(scriptLocation, '.type2.')
    , findFiles(scriptLocation, '.type3.')
]).then(function(type1Files, type2Files, type3Files){
   // all files returned in the first parameter...
})

I like the syntax of the second version, but it doesn't quite do what I want, as the results are not returned individually but rolled up into a single result.

I am using Q as my promise library.

Upvotes: 2

Views: 80

Answers (1)

qwertynl
qwertynl

Reputation: 3933

Use spread instead:

Q.all([
    findFiles(scriptLocation, '.type1.')
    , findFiles(scriptLocation, '.type2.')
    , findFiles(scriptLocation, '.type3.')
]).spread(function(type1Files, type2Files, type3Files){
   // ...
})

From the DOCs:

If you have a promise for an array, you can use spread as a replacement for then. The spread function “spreads” the values over the arguments of the fulfillment handler. The rejection handler will get called at the first sign of failure. That is, whichever of the received promises fails first gets handled by the rejection handler.

Upvotes: 1

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