Category: JavaScript

JavaScript Performance: Variable Initialization

Initializing variables properly in JavaScript can have significant performance benefits. This can be shown with a simple synthetic benchmark.

notype.js

var x = null;

for (var i = 0; i < 1e8; i++) {
    x = 1 + x;
}

withtype.js

var x = 0;

for (var i = 0; i < 1e8; i++) {
    x = 1 + x;
}

Understanding JavaScript: Inheritance and the prototype chain

This is the first post in a series on JavaScript. In this post I’m going to explain how JavaScript’s prototype chain works, and how you can use it to achieve inheritance.

First, it’s important to understand that while JavaScript is an object-oriented language, it is prototype-based and does not implement a traditional class system. Keep in mind that when I mention a class in this post, I am simply referring to JavaScript objects and the prototype chain – more on this in a bit.

Almost everything in JavaScript is an object, which you can think of as sort of like associative arrays - objects contain named properties which can be accessed with obj.propName or obj['propName']. Each object has an internal property called prototype, which links to another object. The prototype object has a prototype object of its own, and so on – this is referred to as the prototype chain. If you follow an object’s prototype chain, you will eventually reach the core Object prototype whose prototype is null, signalling the end of the chain.

HTTP status as a service

Using Node.js* you can run a simple “HTTP status as a service” server. This can be useful for quickly checking whether your application handles various status codes.

var http = require('http');

http.createServer(function (request, response) {
  var status = request.url.substr(1);

  if ( ! http.STATUS_CODES[status]) {
    status = '404';
  }

  response.writeHead(status, { 'Content-Type': 'text/plain' });
  response.end(http.STATUS_CODES[status]);
}).listen(process.env.PORT || 5000);

This will create a server on port 5000, or any port that you specify in the PORT environment variable. It will respond to /{CODE} and return the HTTP status that corresponds to {CODE}. Here’s a couple of examples:

$ curl -i http://127.0.0.1:5000/500
HTTP/1.1 500 Internal Server Error
Content-Type: text/plain
Date: Mon, 30 Sep 2013 14:10:10 GMT
Connection: keep-alive
Transfer-Encoding: chunked

Internal Server Error%

$ curl -i http://127.0.0.1:5000/404
HTTP/1.1 404 Not Found
Content-Type: text/plain
Date: Mon, 30 Sep 2013 14:10:32 GMT
Connection: keep-alive
Transfer-Encoding: chunked

Not Found%

This is a really simple example, and could easily be extended to let you specify a Location header value for 30X responses.

*Well, you could use anything really. I’m just using Node.js since JavaScript is my language of choice.