如果文件已经存在，如何在fs.rename命令上触发错误？

Question

I have the following code that moves files from one directory to another:

var fs = require('fs'),
    oldPath = 'firstfile.txt',
    newPath = 'temp/firstfile.txt';

fs.rename(oldPath, newPath, function (err) {
    console.log('rename callback ', err); 
});

Is it possible to trigger error if newPath file already exists?

Answer 1

Try this peice of Code below:

It called the .exists method which check if a path exists or not

var fs = require('fs'),
    oldPath = 'firstfile.txt',
    newPath = 'temp/firstfile.txt';

fs.exists(newPath, function(exists){
 if (!exists) {
   fs.rename(oldPath, newPath, function (err) {
     console.log('rename callback ', err); 
   });
 } else {
   console.log('The File Already exists');
 }
});

Answer 2

Indeed, you need to do it in one instruction to avoid the race condition (as explained in the comments).

There is at my knowledge no way to do it with the core fs library, but there is a function for doing it in the extended version .

See the move function, whose default behavior doesen't allow to overwride files:

https://github.com/jprichardson/node-fs-extra/blob/master/docs/move.md

const fs = require('fs-extra')

fs.move('/tmp/somefile', '/tmp/does/not/exist/yet/somefile', err => {
  if (err) return console.error(err)

  console.log('success!')
})