Opening and Closing Files

Node.js provides synchronous and asynchronous methods for opening files. Once a file is opened, you can read data from it or write data to it, depending on the flags used to open the file. To open files in a Node.js app, use one of the following statements for asynchronous or synchronous:

Click here to view code image

fs.open(path, flags, [mode], callback)
fs.openSync(path, flags, [mode])

The path parameter specifies a standard path string for your file system. The flags parameter specifies what mode to open the file in—read, write, append, etc., as described in Table 6.1. The optional mode parameter sets the file access mode and defaults to 0666, which is readable and writable.

Table 6.1 Flags that define how files are opened

Once a file has been opened, you need to close it to force flushing changes to disk and release the operating system lock. You close a file by using one of the following methods and passing the file descriptor to it. In the case of the asynchronous close() call, you also need to specify a callback function:

fs.close(fd, callback)
fs.closeSync(fd)

The following is an example of opening and closing a file in asynchronous mode. Notice that a callback function is specified and receives an err and an fd parameter. The fd parameter is the file descriptor that you can use to read or write to the file:

Click here to view code image

fs.open("myFile", 'w', function(err, fd){
  if (!err){
    fs.close(fd);
  }
});

The following is an example of opening and closing a file in synchronous mode. Notice that there is no callback function and that the file descriptor used to read and write to the file is returned directly from fs.openSync():

Click here to view code image

var fd = fs.openSync("myFile", 'w'),
fs.closeSync(fd);