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Learn Javascript

String Processing

Introduction

The string class is another built in class that is slightly different from the normal. Where this class differs from all of the others is the way that you define objects of this type. You have in fact already learned how to do this in the very early tutorials in this series. Any variable that you define as having a text value is automatically a string object and all of the string methods can be applied to it. It is not necesssary to define the object as new String.

String Methods

There are quite a few methods provided by the string class that allow you to manipulate text strings. Some of these methods that you will probably find many uses for include the following:

charAt(number) selects the single character at the specified position within the string
indexOf(substring) finds the position where the specified substring starts
lastIndexOf(substring) finds the last occurrence of the substring within the string
substring(start,end) or substr(start,length) gets the specified part of the string
toLowerCase() convert the string to lowercase
toUpperCase() convert the string to uppercase
split(char) splits the string at each occurrence of the specified character and puts them into an array

You will probably find yourself using these string methods far more than most of the other parts of the Javascript language particularly if you are writing Javascript to validate forms.

Using String Methods

Even though you don't define string objects the way that you do objects belonging to other classes, the way that you access the methods is exactly the same as for other classes in that you specify the name of the object followed by a period and then the name of the method. Let's look at an example:

var txt = 'Some sample text';
document.write(txt.substr(5,6));

This code will print the word sample without the surrounding text (or spaces).

Using What You Know

Suppose that we have a text field containing a number of entries separated by commas that we require to have processed as separate entries. We can easily convert our comma separated list into an array of entries in one simple command like this:

var txt = 'a,b,c,d,e,f,g');
var arry = txt.split(',');

Now arry[0] contains 'a', arry[1] contains 'b', and so on making it easy to then process the entries in the array using a for or while loop.