JavaScript: The Definitive Guide, Fourth Edition

Chapter 11.  Further Topics in JavaScript

This chapter covers miscellaneous JavaScript topics that would have bogged down previous chapters had they been covered earlier. Now that you have read through the preceding chapters and are experienced with the core JavaScript language, you are prepared to tackle the more advanced and detailed concepts presented here. You may prefer, however, to move on to other chapters and learn about the specifics of client-side JavaScript before returning to this chapter.

Data Type Conversion

We’ve seen that JavaScript is an untyped language (or, perhaps more accurately, a loosely typed or dynamically typed language). This means, for example, that we don’t have to specify the data type of a variable when we declare it. Being untyped gives JavaScript the flexibility and simplicity that are desirable for a scripting language (although those features come at the expense of rigor, which is important for the longer, more complex programs often written in stricter languages such as C and Java). An important feature of JavaScript’s flexible treatment of data types is the automatic type conversions it performs. For example, if you pass a number to the document.write( ) method, JavaScript automatically converts that value into its equivalent string representation. Similarly, if you test a string value in the condition of an if statement, JavaScript automatically converts that string to a boolean value -- to false if the string is empty and to true otherwise. ...