This post examines some of the details of how environments are handled in the ECMAScript 5 (ES5) specification [1]. In particular, there isn’t a single “current environment” in ES5, but two: the LexicalEnvironment and the VariableEnvironment. A piece of code at the end exploits these ES5 internals to produce different results on Firefox and Chrome.

This post explains three approaches for extracting information from arrays and objects:

1. for loops,
2. array methods (courtesy of ECMAScript 5 [1]),
3. listing property keys.

It concludes with best practices for applying these approaches.

This post is about converting between primitive values and wrapper objects [1]. Thankfully, one is usually not faced with this kind of task in JavaScript. The most frequent use case is to add properties to a primitive. As a primitive is immutable, you need to convert it to a wrapper object to do so. Read on if you want to see some of JavaScript’s more obscure corners.

Let us start with a short quiz:

What does ({}).valueOf.call(myvar) do?

The Internet Explorer 10 Preview (IE10) comes with many new features, two of them are especially good news for webapp developers:

This post argues that the singleton pattern is usually not needed in JavaScript, because you can directly create objects. It then slightly backpedals from that position and shows you code skeletons that you can use if your needs go beyond the basics.

This post motivates the Singleton design pattern and explains its implementation in Java.

Lifestreams [1] were created in 1996 to correct some of the shortcomings of document management when used for personal information management. Even today, document management is still the dominant way of information management, both conceptually and as a user interface metaphor. Some of the shortcomings are:

With the web’s popularity, it is common for web browsers to have many open tabs at the same time. Processor load can significantly increase in such a case. Google Chrome has implemented several measures to help with that:

Updates:

• [2013-08-08] New blog post: “The flag /g of JavaScript’s regular expressions”
• [2013-08-07] Explained how test() and match() work when the flag g is set.

This post gives an overview of the JavaScript API for regular expressions. It does not, however, go into details about regular expression syntax, so you should already be familiar with it.

HTML5 includes tags for figures and figure captions. This post explains how to use them in modern browsers.