Solve a simple JavaScript problem.

There is JS code:

const fs = require('fs');

// async write

fs.writeFile('hello.txt', 'hello from Node! I am here Another line', function(err) {

if(err) {

console.log('-------');

console.log('Error writing to file.');

console.log('-------');

} else {

console.log('-------');

console.log('1. writing to file is successful.');

console.log('-------');

}

}

);

// async write with __dirname

fs.writeFile(__dirname + '/hello1.txt', 'another hello from Node! I am here Another line', function(err) {

if(err) {

console.log('-------');

console.log('Error writing to file.');

console.log('-------');

} else {

console.log('-------');

console.log('2. writing to file is successful.');

console.log('-------');

}

}

);

// sync write

try {

fs.writeFileSync(__dirname + '/hello2.txt', 'hello from Node!');

console.log('-------');

console.log('3. sync write successful');

console.log('-------');

} catch(err) {

console.log('-------');

console.error('Error writing file.');

console.error(err);

console.log('-------');

}

After I run those code, I got the result as follows:

My question is why output is in "3...1....2..." order? Can you explain it carefully?

3. sync write successful 1. writing to file is successful. 2. writing to file is successful