how to fix this error TypeError [ERR_INVALID_CALLBACK]: Callback must be a function

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无人及你
无人及你 2021-01-03 18:10

I am a beginner to the nodejs. When I type the below, the code error occurs like this:

TypeError [ERR_INVALID_CALLBACK]: Callback must be a function

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  • 2021-01-03 18:21

    Since node 10, it is mandatory to pass a callback on fs.writefile()

    Node.js documented the purpose for the change: https://github.com/nodejs/node/blob/master/doc/api/deprecations.md#dep0013-fs-asynchronous-function-without-callback

    You could add an empty callback like this fs.writeFile('writeMe.txt', data, () => {})

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  • 2021-01-03 18:22

    you also use like this

    var file2 =  fs.readFileSync("./Public/n2.jpeg")
    
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  • 2021-01-03 18:36

    This error hit me in the face when I was doing the following;

    var hello = myfunction( callme() );

    rather than

    var hello = myfunction( callme );

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  • 2021-01-03 18:37

    fs.writeFile(...) requires a third (or fourth) parameter which is a callback function to be invoked when the operation completes. You should either provide a callback function or use fs.writeFileSync(...)

    See node fs docs for more info.

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  • 2021-01-03 18:39
    var fs = require('fs');
    
    fs.readFile('readme.txt', 'utf8', function(err, data) {
        fs.writeFile('writemeee.txt', data, function(err, result) {
    
            if (err) console.log('error', err);
    
        });
    });
    
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  • 2021-01-03 18:41

    Fs.writeFile() according to the documentation here takes ( file, data[, options]and callback ) params so your code will be like this :

     var fs = require('fs');
     fs.readFile('readMe.txt', 'utf8', function (err, data) {
      fs.writeFile('writeMe.txt', data, function(err, result) {
         if(err) console.log('error', err);
       });
     });
    
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