How to write asynchronous functions for Node.js

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I've tried to research on how exactly asynchronous functions should be written. After a lot of plowing through a lot of documentation, it's still unclear to me.

How do I write asynchronous functions for Node? How should I implement error event handling correctly?

Another way to ask my question would be this: How should I interpret the following function?

var async_function = function(val, callback){
    process.nextTick(function(){
        callback(val);
    });
};

Also, I found this question on SO ("How do I create a non-blocking asynchronous function in node.js?") interesting. I don't feel like it has been answered yet.

node.js asynchronous javascript
6 Answers

I've dealing too many hours for such task in for node.js. I'm mainly front-end guy.

I find this quite important, because all node methods asyncronous deal with callback, and transform it into Promise is better to handle it.

I Just want to show a possible outcome, more lean and readable. Using ECMA-6 with async you can write it like this.

 async function getNameFiles (dirname) {
  return new Promise((resolve, reject) => {
    fs.readdir(dirname, (err, filenames) => {
      err !== (undefined || null) ? reject(err) : resolve(filenames)
    })
  })
}

the (undefined || null) is for repl (read event print loop) scenarios, using undefined also work.

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