node.js basic file operations and notes

• Modular:

  In node in a js is a module.

  ) Referenced by external modules require (. If the path is relative, or ./ .. need to begin.

  A file is a module, there is an imaginary function wrapped, so I want to call on the outside, you need to use export.x

• The module may include references

  • The core module directly write the name on the list.

  For example, it fs module

  • File module

• js in the window here is global

• Recommended module.exports.xxx way, we can declare external calls.

• Some operations of npm

  • npm -v view the version of npm
  • npm version View all versions of the modules
  • npm search package name search name
  • npm install package name installation (i may be used instead of install)
  • npm install package name --save installation package dependencies and added to
  • npm remove the package name to delete package (can substitute r remove)
  • npm install download the current project depends package
  • npm install -g global installed package package name (usually the tool)

• Node basis

  • The concept of buffer zone buffer

    var buf = Buffer.from(str);
    var buf2 = Buffer.alloc(10);
    

    • After determining the size of the buffer is not modified.

    • The actual hexadecimal memory, but so will the real output to the console into a decimal.

    • Buffer.from (str) into a string buffer

    • Buffer.toString () of the data buffer into a string

  • File system

    • Files by node to operate the system.

    • var fs = require("fs");
      

    • Usually two groups, with a sync synchronization, without asynchronous.

    • Write sync file

    • var fd = fs.openSync("xxx.txt", "w");
      fs.writeSync(fd, "今天天气不错");
      fs.closeSync(fd);
      

    • Asynchronous file write

      • Relatively good performance
      • The results returned by the callback function
      • The callback function takes two parameters:
        • err error object
        • file descriptor fd
      • Asynchronous later are performed after the code in the callback function

    • //多一个回调函数 ，异步方法没有返回值
      fs.open("xxx2.txt", "w",function(err, fd){
          if(!err){
      			fs.write(fd, "今天天气不错" ,function(err){
              if(!err){
                .写入成功.
              }
            });
      			fs.closeSync(fd,function(err){
              if(!err){
                 .文件成功关闭.
              }
            });
          }else {
            console.log(err);
          }
      });
      

    • Simple file write

      • var fs = require("fs");
        fs.writeFile("hello3.txt", "这是通过writeFile写入的内容",{flag:"w"},function(err){
          if(!err){
            console.log("写入成功...");
          }
        });
        

    • Streaming files are written

      • Written for large files

      • on (Event String, callback)

      • once (Event String, callback) to bind a one-off

      • var ws = fs.createWriteStream("Hello3.txt");
        ws.once("open", function(){
          console.log("233");
        })
        ws.once("close", function(){
          console.log("233");
        })
        ws.write("通过可写流写入文件的内容");
        ws.write("通过可写流写入文件的内容");
        ws.write("通过可写流写入文件的内容");
        
        ws.end();
        //不要用ws.close()，拔掉水管的那一头
        

    • Synchronize files to read

    • Asynchronous file read

    • Simple file read

      var fs = require("fs");
      fs.readFile("hello3.txt", function(err, data){
        if(!err) {
          console.log(data);
      		//也可以整合上面的writeFile
        }
      })
      

    • Streaming file read

      • It can be divided into multiple times to read a large file into memory.

      • var fs = require("fs");
        var rs = fs.createReadStream("an.jpg");
        //监听流的开启和关闭
        rs.once("open", function(){
          console.log("可读流打开了～～～")；
        });
        rs.once("close", function(){
          console.log("可读流关闭了～～～")；
        });
        
        //为data绑定事件，就可以自动运行
        rs.on("data", function(){
          //实现复制的效果。
          ws.write(date);
        });
        
        //传输数据，还可以用pipe简化
        rs.pipe(ws);
        

    • Some other methods of file operations

      • fs.stat("a.mp3", function(err, stat){
        	//查看是不是文件、目录
          console.log(stat.isFile());
          console.log(stat.isDirectory());
          
        });
        //删除文件
        fs.unlinkSync("hello.txt");
        //读取当前文件目录结构
        fs.readdir(".", function(err, files){
          if(!err){
            console.log(files);
          }
        });
        
        //截断文件,将文件前3个留下来。
        fs.truncateSync("hello2.txt", 3);
        //创建文件夹
        fs.mkdirSync("hello");
        //删除文件夹
        fs.rmdirSync("hello");
        //重命名,前两个是目录字符串
        fs.rename("a.mp3", "笔记.mp3",function(err) {
          if(!err){
            console.log("修改成功～～～");
          }
        });
        
        //监视文件的修改，回调函数，当文件发生变化的，被执行。
        //运行起来，就会一直运行，不会停。
        //拥有定时机制
        fs.watchFile("hello2.txt",{interval:1000},function(curr, prev){
          //上面两个参数，都是stat类型的。
          console.log("文件发生了变化");
        });