NodeJS 是否总是/自动异步运行代码？

Question

I am new to this Node.js. And I am afraid all of my code will run synchronously thus blocking the other requests makes my app laggy, freezing, etc when handling many request.

If I write this code:

const array = new Array(1000000000);

for (let i=0; i < array.length; i++) {
  const item = array[i];
  // do a lot heavy lifting with each item
}

Will Node.js automatically run that code asynchronously?

Will it block other requests while it still run that code?

Or should I explicitly declare async/await on every piece of my code?

Answer 1

You can declare

• async only for a function
• await only for a Promise (if not, Node will automatically wrap your code in a Promise)

As long as you don't have any Promises, your code will be synchronous (you can think of it as Java or Python)

Callbacks are not necessarily async as well, they are just functions and they run depending on the implementation of the function they are provided.

A.then(B) will run in an async fashion, where A is a Promise and B will run after the current execution ends

Answer 2

That particular code will always run synchronously and will block all other script activity.