Node.js fs.writeFileSync()方法用法示例指南

Node.js的" fs"模块实现了文件I / O操作。 fs模块中的方法可以是同步的, 也可以是异步的。异步函数具有作为最后一个参数的回调函数, 该参数指示异步函数的完成。与异步方法相比, Node.js开发人员更喜欢异步方法, 因为异步方法在执行过程中从不阻塞程序, 而后者则不会。阻塞主线程是Node.js中的不当行为, 因此同步功能应仅用于调试或在没有其他选项可用时使用。 fs.writeFileSync()是一种同步方法。如果指定的文件不存在, 则fs.writeFileSync()将创建一个新文件。此外, " readline-sync"模块用于在运行时启用用户输入。

语法如下：

fs.writeFileSync( file, data, options )

参数：此方法接受上述和以下所述的三个参数：

• 文件：它是一个字符串, Buffer, URL或文件描述整数, 表示必须在其中写入文件的路径。使用文件描述符将使其行为类似于fs.write()方法。
• 数据：它是将写入文件的字符串, Buffer, TypedArray或DataView。
• 选项：它是一个字符串或对象, 可用于指定将影响输出的可选参数。它具有三个可选参数：
  • 编码：它是一个字符串, 它指定文件的编码。默认值为" utf8"。
  • 模式：它是一个整数, 指定文件模式。默认值为0o666。
  • flag：它是一个字符串, 指定在写入文件时使用的标志。默认值为" w"。

以下示例说明了fs.writeFileSync()方法在Node.js中：

范例1：

// Node.js program to demonstrate the
// fs.writeFileSync() method
  
// Import the filesystem module
const fs = require( 'fs' );
  
let data = "This is a file containing a collection"
            + " of programming languages.\n"
  + "1. C\n2. C++\n3. Python" ;
  
fs.writeFileSync( "programming.txt" , data);
console.log( "File written successfully\n" );
console.log( "The written has the following contents:" );
console.log(fs.readFileSync( "programming.txt" , "utf8" ));

输出如下：

File written successfully

The written has the following contents:
This is a file containing a collection of programming languages.
1. C
2. C++
3. Python

范例2：

// Node.js program to demonstrate the
// fs.writeFileSync() method
  
// Import the filesystem module
const fs = require( 'fs' );
  
// Writing to the file 5 times
// with the append file mode
for (let i = 0; i < 5; i++) {
   fs.writeFileSync( "movies.txt" , "Movie " + i + "\n" , {
       encoding: "utf8" , flag: "a+" , mode: 0o666
     });
}
  
console.log( "File written successfully 5 times\n" );
console.log( "The written file has the following contents:" );
console.log(fs.readFileSync( "movies.txt" , "utf8" ));

输出如下：

File written successfully 5 times

The written file has the following contents:
Movie 0
Movie 1
Movie 2
Movie 3
Movie 4

参考： https://nodejs.org/api/fs.html#fs_fs_writefilesync_file_data_options

范例3：使用readline模块从用户获取运行时输入的文件名和文件数据

// Write Javascript code here
var readline = require( 'readline-sync' ); 
var fs = require( "fs" ); 
    
var path = readline.question( "Enter file name/path: " ); 
  
console.log( "Entered path : " + path); 
  
var data = readline.question( "Enter file data: " );
  
//synchronous functions may throw errors 
//which can be handled using try-catch block
try {
   fs.writeFileSync(path, data, {flag: 'a+' });   //'a+' is append mode
   console.log( "File written successfully" );
} catch (err) {
   console.error(err);
}
console.log( "-----------------------------------------------" );
try {
const data = fs.readFileSync(path, {encoding: "utf8" }); 
   console.log( "File content is as follows:" );
   // Display the file data 
   console.log(data); 
} catch (err){
console.log(err);
}

输出如下

范例4：使用缓冲区使用readline模块从用户获取运行时输入的文件数据

// Write Javascript code here
var fs = require( "fs" );
var readline = require( 'readline-sync' ); 
var path = readline.question( "Enter file name/path: " ); 
  
console.log( "Entered path : " + path); 
// 1024 specifies the buffer size. We can limit 
// the data size by this approach
var buf = new Buffer.alloc(1024);
buf = readline.question( "Enter data:" );
  
  
try {
   fs.writeFileSync(path, buf, {flag: 'a+' });
   console.log( "File written successfully" );
} catch (err) {
   console.error(err);
}
console.log( "-----------------------------------------------" );
try {
const data = fs.readFileSync(path, {encoding: "utf8" }); 
   console.log( "File content is as follows:" );
   // Display the file data 
   console.log(data); 
} catch (err){
console.log(err);
}

输出如下

---