fswriteFileSync

fswriteFileSync is the synchronous counterpart to the Node.js file system write operation. It is a function in the built-in fs module that writes data to a file and blocks the event loop until the operation completes. If the target file already exists, its contents are replaced unless a different flag is specified.

The typical signature is fs.writeFileSync(file, data, options). The file parameter can be a path string, a Buffer, or a URL. The data parameter is a string or a Buffer (or Uint8Array). The options parameter can be a string encoding or an options object. When a string is provided, it specifies the encoding used for writing if data is a string. When an options object is used, it can include encoding, mode, and flag. The default flag is 'w', which writes and truncates the file. The default encoding is 'utf8' for string data.

Behavior and errors: The call throws an exception on failure instead of using a callback. Common errors include ENOENT for missing directories, EACCES for insufficient permissions, or EISDIR if a directory path is supplied where a file is expected. Wrap calls in try/catch to handle errors gracefully.

Usage considerations: Because it blocks the event loop, writeFileSync is best suited for startup scripts, CLI tools, or other non-concurrent tasks. For non-blocking operations, use the asynchronous fs.writeFile or the equivalent Promises API.

Example: fs.writeFileSync('example.txt', 'Hello world', 'utf8'); You can also pass an options object: fs.writeFileSync('example.txt', data, { encoding: 'utf8', mode: 0o644, flag: 'w' });