Fastest way to copy file in node.js

This is a good way to copy a file in one line of code using streams:

var fs = require('fs');

fs.createReadStream('test.log').pipe(fs.createWriteStream('newLog.log'));

Same mechanism, but this adds error handling:

function copyFile(source, target, cb) {
  var cbCalled = false;

  var rd = fs.createReadStream(source);
  rd.on("error", function(err) {
    done(err);
  });
  var wr = fs.createWriteStream(target);
  wr.on("error", function(err) {
    done(err);
  });
  wr.on("close", function(ex) {
    done();
  });
  rd.pipe(wr);

  function done(err) {
    if (!cbCalled) {
      cb(err);
      cbCalled = true;
    }
  }
}

I was not able to get the createReadStream/createWriteStream method working for some reason, but using fs-extra npm module it worked right away. I am not sure of the performance difference though.

fs-extra

npm install --save fs-extra

var fs = require('fs-extra');

fs.copySync(path.resolve(__dirname,'./init/xxx.json'), 'xxx.json');

Mike Schilling's solution with error handling with a short-cut for the error event handler.

function copyFile(source, target, cb) {
  var cbCalled = false;

  var rd = fs.createReadStream(source);
  rd.on("error", done);

  var wr = fs.createWriteStream(target);
  wr.on("error", done);
  wr.on("close", function(ex) {
    done();
  });
  rd.pipe(wr);

  function done(err) {
    if (!cbCalled) {
      cb(err);
      cbCalled = true;
    }
  }
}

Fast to write and convenient to use, with promise and error management.

function copyFile(source, target) {
    return new Promise(function(resolve, reject) {
        var rd = fs.createReadStream(source);
        rd.on('error', reject);
        var wr = fs.createWriteStream(target);
        wr.on('error', reject);
        wr.on('finish', resolve);
        rd.pipe(wr);
    });
}

Well, usually it is good to avoid asynchronous file operations. Here is the short (i.e. no error handling) sync example:

var fs = require('fs');
fs.writeFileSync(targetFile, fs.readFileSync(sourceFile));