b.js

console.log('L1');
setTimeout(() => console.log('L2'), 0);
new Promise((resolve) => {
  console.log('L3');
  setImmediate(() => console.log('L4'));
  process.nextTick(() => console.log('L5')) // node backend only  
  resolve();
})
.then(() => console.log('L6'));
console.log('L7');