[Node.js] The difference between synchronization and asynchronousness

In order to use Node.js for file operations, you must first use require('fs') to load the file system template. The last parameter of the asynchronous method is a complete callback function (callback function). The parameters passed to the callback function generally depend on the method itself, but the first parameter is always an exception (err). If the method executes successfully, the first parameter will be null or undefined. When executing using synchronous methods, any exceptions are raised immediately. We can use try or catch to handle exceptions and display error information.

Gives an example of an asynchronous method, where there is a hello file in the tmp folder.

This code will delete the hello file in the tmp directory. If the deletion is successful, the successful deletion information will be printed in the console.

引入fs模块
const fs=require("fs");
//异步操作读取文件
fs.unlink('./tmp/hello',(err)=>{
    if(err) throw err;
    console.log('成功删除hello文件');
});

You can also use asynchronous methods to achieve the same function.

引入fs模块
const fs=require("fs");
//同步操作读取文件
fs.unlinkSync('./tmp/hello');
console.log('成功删除hello文件');

Asynchronous operation methods cannot guarantee successful execution, so the order of file operations is very important during code execution.

For example: the following code will cause an error

//重命名hello文件为world文件
fs.rename('./tmp/hello','./tmp/world',(err)=>{
  if(err) throw err;
  console.log('renamed complete');
});
//获取world文件的信息
fs.stat('./tmp/world',(err)=>{
  if(err) throw err;
    console.log(`stats:${JSON.stringify(stats)}`);
});

fs.stat will be executed before fs.rename. The correct method is Use callback function to execute.

The following is the correct use of callback functions to handle exceptions during program execution:

fs.rename('./tmp/hello','./tmp/world',(err)=>{
    if(err) throw err;
    fs.stat('./tmp/world',(err,stats)=>{
        if(err) throw err;
        console.log(`stats:${JSON.stringify(stats)}`);
    });
});

Note: In a large system, it is recommended to use asynchronous methods , the synchronization method will cause the process to be locked. Compared with synchronous methods, asynchronous methods are more performant, faster, and less blocking.

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