Node3-4 base API ---- fs (file system)

Asynchronous form always completion callback as its last argument . Pass completion callback parameters depend on the specific method, but the first parameter is always reserved for abnormalities . If the operation is completed successfully, the first argument will be null or undefined.

1. Read the file operation (readFile)

For example (file read operation) will first synchronization after executing [try to use asynchronous]

the require FS = const ( 'FS' ) 
fs.readFile ( './30_readfile.js', 'UTF8', (ERR, Data) => {
     IF (ERR) {
         the throw ERR 
    } the else {
         // The output is a Buffer (because there is no toString or parameters define the encoding format) 
        the console.log (Data);
         // the console.log (data.toString ()); 
    } 
}) 

// synchronization 
const data = fs.readFileSync ( './ 29_event_remove.js', 'UTF8' ); 
the console.log (Data);

2. Write file ( writeFile )

//输出done
const fs = require('fs')

fs.writeFile('./text','this is text','utf8',err=>{
    if(err) throw err;
    console.log('done')
})

//输出done 使用了Buffer
const fs = require('fs')
const content = Buffer.from('this is text')
fs.writeFile('./text',content,err=>{
    if(err) throw err;
    console.log('done')
})

3. view the file information (stats)

const fs =require('fs')
fs.stat('./32_stat.js',(err,stats)=>{
    if(err){
        throw err
    }else{
        console.log(stats.isFile());
        console.log(stats.isDirectory());
        console.log(stats);
    }
})

operation result:

4. Rename (the rename)

const fs =require('fs')
fs.rename('./text','text.txt',err=>{
    if(err) throw err
    console.log('done!');
})

5.unlink

const fs = require('fs')
fs.unlink('./text.txt',err=>{});

6. Read folder (readdir)

const fs = require('fs')
fs.readdir('./',(err,files)=>{
    if(err) throw err
    console.log(files);
})

operation result

7. Create a folder (mkdir)

const fs =require('fs')
fs.mkdir('test',err=>{ })

8. Remove a folder (rmdir)

const fs = require('fs')
fs.rmdir('./test',err=>{});

9. Monitoring (Watch) [useful, as the local build very convenient]

const fs = require('fs')
fs.watch('./',{
    recursive:true
},(eventType,filename)=>{
    console.log(eventType,filename);
});

10.readstream

// Stream directional flow (data) by Stream There are two conditions, one is a data direction 
const the require FS = ( 'FS' ) 
const RS = fs.createReadStream ( './ 39_readstream.js' );
 // to read a little bit, similar to loading from top to bottom Suman 
rs.pipe (process.stdout);

11.writestream

const fs =require('fs')
const ws = fs.createWriteStream('./text.txt')
const tid = setInterval(()=>{
    const num = parseInt(Math.random()*10)
    console.log(num);
    
    if(num<8){
        ws.write(num + '')
    }else{
        clearInterval(tid)
        ws.end()
    }
},200)
ws.on('finish',()=>{
    console.log('done!'); 
})

operation result

12. callback hell resolved

method one

const fs =require('fs')
const promisify = require('util').promisify;

const read = promisify(fs.readFile)
read('./41_promisify.js').then(data=>{
    console.log(data.toString());
    
}).catch(ex=>{
    console.log(ex);
    
})

operation result

Method Two

const fs =require('fs')
const promisify = require('util').promisify;

const read = promisify(fs.readFile)
// read('./41_promisify.js').then(data=>{
//     console.log(data.toString());
    
// }).catch(ex=>{
//     console.log(ex);
    
// })

async function test(){
    try{
        const content= await read('./41_promisify.js')
        console.log(content.toString());
    }catch(ex){
        console.log(ex);
    }   
}
test();

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Node3-4 base API ---- fs (file system)

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