Instructions for the fs.writeFile method in node.js

method description:

Write data to a file asynchronously, and if the file already exists, the original content will be replaced.

syntax:

fs.writeFile(filename, data, [options], [callback(err)])

Since this method belongs to the fs module, it is necessary to introduce the fs module (var fs= require(" fs "))

before using it

receive parameters:

filename         (String)                  

data               (String | Buffer)       is going to write something that can make a string or buffer data.

options           (Object

· encoding     (string)                 optional value, default 'utf8', when data buffer, the value should be ignored.

· mode                   (Number)           file read and write permissions, default value of 438

flag               The default value of     is' w'

callback {Function}   callback, passing an exception parameter err.

example:

fs.writeFile('message.txt', 'Hello Node', function (err) {

  if (err) throw err;

  console.log('It\'s saved!');

});

source:

fs.writeFile = function(path, data, options, callback) {

  var callback = maybeCallback(arguments[arguments.length - 1]);

  if (util.isFunction(options) || !options) {

    options = { encoding: 'utf8', mode: 438 /*=0666*/, flag: 'w' };

  } else if (util.isString(options)) {

    options = { encoding: options, mode: 438, flag: 'w' };

  } else if (!util.isObject(options)) {

    throw new TypeError('Bad arguments');

  }

  assertEncoding(options.encoding);

  var flag = options.flag || 'w';

  fs.open(path, options.flag || 'w', options.mode, function(openErr, fd) {

    if (openErr) {

      if (callback) callback(openErr);

    } else {

      var buffer = util.isBuffer(data) ? data : new Buffer('' + data,

          options.encoding || 'utf8');

      var position = /a/.test(flag) ? null : 0;

      writeAll(fd, buffer, 0, buffer.length, position, callback);

    }

  });

};