Async/sync

Code synchrone / bloquant 

1. const { readFileSync, writeFileSync } = require('fs')
2. console.log('start')
3. const first = readFileSync('./content/first.txt', 'utf8')
4. const second = readFileSync('./content/second.txt', 'utf8')
5. 
   
6. writeFileSync(
7.   './content/result-sync.txt',
8.   `Here is the result : ${first}, ${second}`,
9.   { flag: 'a' }
10. )
11. console.log('end')
12. console.log('new')

Code asynchrone / non bloquant  

1. const { readFile, writeFile } = require('fs')
2. 
   
3. console.log('start')
4. readFile('./content/first.txt', 'utf8', (err, result) => {
5.   if (err) {
6.     console.log(err)
7.     return
8.   }
9.   const first = result
10.   readFile('./content/second.txt', 'utf8', (err, result) => {
11.     if (err) {
12.       console.log(err)
13.       return
14.     }
15.     const second = result
16.     writeFile(
17.       './content/result-async.txt',
18.       `Here is the result : ${first}, ${second}`,
19.       (err, result) => {
20.         if (err) {
21.           console.log(err)
22.           return
23.         }
24.         console.log('end')
25.       }
26.     )
27.   })
28. })
29. 
    
30. console.log('new')

Code asynchrone / non bloquant / promese

1. const { readFile, writeFile } = require('fs').promises
2. 
   
3. console.log('start');
4. let result = "";
5. readFile('./content/first.txt', 'utf8')
6.   .then((text) => {
7.     result = result.concat(text);
8.     return readFile('./content/second.txt', 'utf8')
9.   })
10.   .then((text) => {
11.     result = result.concat(text);
12.     writeFile('./content/promise.txt', `result: ${result}`, { flag: 'a' })
13.   })
14.   .then(() => console.log('end'))
15.   .catch((err) => console.log(err))
16. console.log('new');

Code asynchrone / non bloquant / async

1. const { readFile, writeFile } = require('fs').promises
2. 
   
3. console.log('start');
4. const start = async () => {
5.   try {
6.     const first = await readFile('./content/first.txt', 'utf8')
7.     const second = await readFile('./content/second.txt', 'utf8')
8.     await writeFile('./content/async.txt',`result : ${first} ${second}`,{ flag: 'a' })
9.     console.log('end');
10.   } catch (error) {
11.     console.log(error)
12.   }
13. }
14. 
    
15. start()
16. console.log('new');

Notez le code exécuté en paralléle.

const { readFile, writeFile } = require('fs').promises

console.log('start');

const read1 = readFile('./content/first.txt', 'utf8')

const read2 = readFile('./content/second.txt', 'utf8')

Promise.all([read1, read2]).then((values) => {

  writeFile('./content/promise.txt', `result: ${values.join(" ")}`, { flag: 'a' })

  console.log('end');

});

console.log('new');