Nodejs 笔记

秒速五厘米 2023-02-21 12:54 24阅读 0赞

**Nodejs 笔记**

--------------------

*  **event Module**

*  **readline Module**

//ReadLine Module的作用是获取用户输入，还能向用户提示程序的输出，即构建用户交互界面。
    const readline = require('readline');
    const rl = readline.createInterface({ input : process.stdin,output : process.stdout});
    
    //Math.random()可以用于生成0-1（不含1）之间的随机数
    let num1 = Math.floor(Math.random()*10 + 1);
    let num2 = Math.floor(Math.random()*10 + 1);
    let answer = num1 + num2;
    
    //rl.question()方法将query写入output，并等待用户在input上提供输入。
    //然后调用callback，将用户输入作为回调的第一个参数
    rl.question(`What is ${ num1 } + ${ num2 }? \n`,(userInput)=>{ 
        //trim()方法的作用是去掉用户输入（userInput）的前后空格
        if(userInput.trim() == answer){ 
            rl.close();
        }else{ 
            rl.setPrompt('False Result Please try again.\n');
            rl.prompt();
            //用户按下回车将触发line事件
            rl.on('line',(userInput)=>{ 
                if(userInput.trim() == answer){ 
                    rl.close();
                }else{ 
                    rl.setPrompt(`Your answer ${ userInput} is incorrect,please try again.\n`);
                    rl.prompt();
                }
            })
        }
    });
    
    rl.on('close',()=>{ 
        console.log('True');
    });

*  **FileSystem Module**

const fs = require('fs');

//创建文件
    fs.writeFile('example.txt','this is a example',(err)=>{ 
        if(err){ 
            console.log('err');
        }else{ 
            console.log('File successfully created');
            //读取文件
            fs.readFile('example.txt','utf8',(err,file)=>{ 
                if(err){ 
                    console.log(err);
                }else{ 
                    console.log(file);
                }
            })
        }
    })

//重命名文件
    fs.rename('example.txt','example2.txt',(err)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log('File successfully renamed');
        }
    })

//文件追加内容
    fs.appendFile('example2.txt',', Some data been appended',(err)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log('File successfully appended.');
        }
    })

//删除文件
    fs.unlink('example2.txt',(err)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log('File successfully deleted.');
        }
    })

//创建文件夹
    fs.mkdir('tutorial',(err)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log('folder successfully created');
        }
    })

//删除文件夹(只对空文件夹有效)
    fs.rmdir('tutorial',(err)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log('folder successfully deleted');
        }
    })

//创建文件夹的同时创建文件
    fs.mkdir('tutorial',(err)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log('folder successfully created');
            //注：这里的./表示js文件所在目录
            fs.writeFile('./tutorial/example.txt','12345678',(err)=>{ 
                if(err){ 
                    console.log(err);
                }else{ 
                    console.log('file successfully created')
                }
            })
        }
    })

//读取文件夹，遍历删除文件
    fs.readdir('tutorial',(err,files)=>{ 
        if(err){ 
            console.log(err);
        }else{ 
            console.log(files);
            for(let file of files){ 
                fs.unlink('./tutorial/'+file,(err)=>{ 
                    if(err){ 
                        console.log(err);
                    }else{ 
                        console.log(`successfully deleted the file ${ file}`);
                    }
    
                })
            }
        }
    })

*  **流式读取文件**

const fs = require('fs');
    //普通读取文件的方式会将整个文件读入内存缓冲区，如果文件过大将无法读取
    //流式读取文件，不用等待文件完全加载即可操作，而是把文件分成小块进行缓冲
    //效率更高，对内存需求少。
    const readStream = fs.createReadStream('./example.txt','utf8');
    const writeStream = fs.createWriteStream('./example2.txt');
    //读取文件时将触发data事件，chunk指分块的文件。
    readStream.on('data',(chunk)=>{ 
    	console.log(chunk);
    	writeStream.write(chunk);
    	console.log('文件写入成功！')
    });

**注：以上内容和以下内容等价**

const fs = require('fs');
    const readStream = fs.createReadStream('./example.txt','utf8');
    const writeStream = fs.createWriteStream('./example2.txt');
    //管道操作，源头.pipe(目的)
    readStream.pipe(writeStream);

*  压缩和解压

//压缩
    const fs = require('fs');
    const zlib = require('zlib');
    const readStream = fs.createReadStream('./example.txt','utf8');
    const writeStream = fs.createWriteStream('./example2.gz');
    const gzip = zlib.createGzip();
    readStream.pipe(gzip).pipe(writeStream);

//解压
    const fs = require('fs');
    const zlib = require('zlib');
    const readStream = fs.createReadStream('./example2.gz');
    const writeStream = fs.createWriteStream('./uncompressed.txt');
    const gunzip = zlib.createGunzip();
    readStream.pipe(gunzip).pipe(writeStream);

*  **http Module**

*  **静态资源托管**

const http = require('http');
    const fs = require('fs');
    http.createServer((req,res)=>{ 
        const readStream = fs.createReadStream('./static/baidu.png');
        res.writeHead(200,{ 'Content-type':'image/png'});
        readStream.pipe(res);
    }).listen(3000);

const http = require('http');
    const fs = require('fs');
    http.createServer((req,res)=>{ 
        const readStream = fs.createReadStream('./static/index.html');
        res.writeHead(200,{ 'Content-type':'text/html'});
        readStream.pipe(res);
    }).listen(3000);

const http = require('http');
    const fs = require('fs');
    http.createServer((req,res)=>{ 
        const readStream = fs.createReadStream('./static/example.json');
        res.writeHead(200,{ 'Content-type':'application/json'});
        readStream.pipe(res);
    }).listen(3000);

*  **npm init**

**npm init 可用来初始化生成一个新的 package.json 文件：**

{ 
      "name": "src",
      "version": "1.0.0",
      "description": "BLU",
      "main": "app.js",
      "scripts": { 
        "test": "echo \"Error: no test specified\" && exit 1"
      },
      "author": "BLU",
      "license": "ISC",
      "dependencies": { }
    }

*  **npm install**

npm install 命令用来安装模块  
示例：

npm install lodash