CODEWITHSUNDEEP
javascriptnode.jscallbackdownload
Hard Tacos
Hard Tacos

Reputation: 370

Javascript Callback Functions - Node.js

I have two functions,

1) download(uri, filename, callback) -> Downloads an image to a specific location
2) twitterPost(filename) -> Tweets the image

I need to do this Asynchronously - so I call twitterPost after the image is done downloading, however I receive this error every time: 

throw new Error('File path does not exist: ' + media);                                                                                                               
      ^                                                                                                                                                              
Error: File path does not exist: Imgs/18478-wrt1114.jpg

Now I understand that this is appearing because the image has not downloaded, however it doesn't make sense seeing that the callback function is called after the pipe is closed. Here is my code for both functions:

function download(uri, filename, callback) {
    request.head(uri, function(err, res, body) {
        request(uri).pipe(fs.createWriteStream(filename)).on('end', callback);
    });
};

and

function twitterPost(filename) {

    var twitterRestClient = new Twitter.RestClient(
        // API KEYS AND STUFF HERE
    );

    twitterRestClient.statusesUpdateWithMedia(
        {
            'status': 'Test Tweet',
            'media[]': filename
        },
        function(error, result) {
            if (error) { console.log('Error: ' + error.message) }

            if (result) { console.log(result.text) }
    });
}

Here is my function call:

download(image, filename,twitterPost(filename));

Am I using callbacks incorrectly, or is there some other issue that I am not noticing causing this problem

Thank you for you help!

Upvotes: 1

Views: 112

Answers (2)

Bergi
Bergi

Reputation: 665555

Am I using callbacks incorrectly

Yes, you're not actually passing a callback function. You pass the result of immediately invoking twitterPost(filename) - which happens even before download is invoked, so there is no such file yet.

Use a function expression around this call, to get that function called by download:

download(image, filename, function(endEvent) {
    twitterPost(filename);
});

Upvotes: 2

sdumetz
sdumetz

Reputation: 562

I think your problem is due to the way you pass arguments to your function.

download(image, filename,twitterPost(filename));

check in twitterPost(filename) that your filename is as expected. I'm pretty sure it wont. That's because your twitterPost function is not called with this argument. It is called with :

request(uri).pipe(fs.createWriteStream(filename)).on('end', callback);

that is, no arguments. I'd do :

request(uri).pipe(fs.createWriteStream(filename)).on('end', function(){
  callback(filename);
});

Upvotes: -1

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