why nodejs file system read console first then read the file-CodePudding

I can read the files using nodejs file system:

const fs = require('fs');

fs.readFile('./assets/test1.txt', (err, data) => {
    if(err){
        console.log(err)
    }
    console.log(data.toString())
})

console.log('hello shawn!')

Why console.log('hello shawn!') read first times then read the console.log(data.toString())?

Is there any other things in file system read data first then read below console?

CodePudding user response：

It is because .readFile is a asynchronous operation. Its last parameter is callback function, which is started after operation is done. I recommend read something about callbacks and event loop.

You can use a synchronous version of function readFileSync or use utils.promisify to convert callback function to promise and use async/await then example.