JavaScript: The Missing Manual

Chapter 4. Working with Words, Numbers, and Dates

Storing information in a variable or an array is just the first step in effectively using data in your programs. As you read in the last chapter, you can use data to make decisions in a program (“Is the score 0?”). You’ll also frequently manipulate data by either searching through it (trying to find a particular word in a sentence, for example), manipulating it (rounding a number to a nearest integer), or reformatting it to display properly (formatting a number like 430 to appear in the proper monetary format, like $430.00).

This chapter will show you how to accomplish common tasks when working with strings and numbers. In addition, it’ll introduce the JavaScript Date object, which lets you determine the current date and time on a visitor’s computer.

A Quick Object Lesson

So far in this book, you’ve learned that you can write something to a Web page with the document.write() command, and to determine how many items are in an array, you type the name of the array followed by a period and the word “length,” like so: days.length. You’re probably wondering what those periods are about. You’ve made it through three chapters without learning the particulars of this feature of JavaScript syntax, and it’s time to address them.

You can conceptualize many of the elements of the JavaScript language, as well as elements of a Web page, as objects. The real world, of course, is filled with objects too, such as a dog or a car. Most objects are made ...