如何将此阻塞代码重构为对node.js非阻塞

Question

I need to refactor this code to non blocking.

I have wrote a simple helper code, What this does is generates invoice Number based on provided previous number.

helper.js

module.exports = {
  replaceCharAt: function replaceCharAt(string, index, character){
    var string = string.split('');
    string[index] = character;
    return string.join('');
  },
  generateInvoiceNumber: function generateInvoiceNumber(invoiceNumber, useIndex){
    var invoiceNumber = invoiceNumber.trim();
    if(typeof useIndex === 'undefined' || useIndex === -1 ){
      useIndex = invoiceNumber.length - 1;
    }
    var incrementChar = invoiceNumber[useIndex];
    if(incrementChar == '9' || incrementChar == 'z' || incrementChar == 'Z'){
      if(incrementChar == 9){
        invoiceNumber = this.replaceCharAt(invoiceNumber, useIndex, '0');
      }
      else{
        invoiceNumber = this.replaceCharAt(invoiceNumber, useIndex, 'a');
      }
      if(useIndex === 0){
        return invoiceNumber = '1'+invoiceNumber;
      }
      return this.generateInvoiceNumber(invoiceNumber, useIndex - 1);
    }
    else{
      var replaceChar = String.fromCharCode(incrementChar.charCodeAt(0) + 1);
      invoiceNumber = this.replaceCharAt(invoiceNumber, useIndex, replaceChar);
    }
    return invoiceNumber;
  }
};

How I use it in request handler.

var helper = require('./helper');

var handler = function(request, reply){
  var newNumber = helper.generateInvoiceNumber(request.params.oldNumber);
  reply({newNumber: newNumber});
}

So this code blocks until it generates the Invoice number. I need some tips and hints on how to refactor this to not block.

Answer 1

Since your code is all synchronous by nature, eg: you're not making any IO calls, there's no way for you to make this code async :(

Async code must be making IO calls, stuff like this:

• Writing to disk.
• Talking over the network.
• Calling subprocesses and waiting for responses.

These things can all be made asynchronous because your program is simply waiting for some other piece of hardware to do something: process results, send responses, etc.

In your code, you're simply performing some CPU operations: if statements, string comparisons, etc. This stuff always has to be processed by your CPU directly, and since that's the case, there's no way for you to 'wait for that to finish', so to speak.

If you're really intent on making this async, you could do the following:

• Write an API service that performs those synchronous tasks.
• Expose that API service over the network: http://blah.com/api
• Rewrite your local Node code to make async calls to that API and wait for the results.

The truth, however, is that since your code is pretty minimally synchronous, you shouldn't need to do the above. All projects have some synchronous code in them -- there's no escaping it =)