Server Side JavaScript and File Manipulation

by Thomas Valentine

This short tutorial will show you the most common methods for file manipulation in JavaScript

When designing your server side JavaScript script for your site, you may realize the need to access and manipulate not only your databases, but simple files as well. Server side JavaScript has recognized this and created the "File" object. With it you may read and write to simple files, the most common being ASCII text files (.txt extension). There are eighteen methods which pretty much covers all of the functionality you'll need in working with your files on the server from the web site pages. They are as follows:

• byteToString() - This method converts the byte numbers passed as the parameter to the method into its textual, string equivalent.
• clearError() - This method is used to clear the "file error" status on a file stated within the file.eof and file.error log files.
• close() - This method is used to simply close the file which you opened and possibly worked with earlier.
• eof() - This method is used to tell you if you are at the end of the file you have opened and are using. "EOF" means End Of File.
• error() - This method returns the current error, if any.
• exists() - This method is used to tell you if the file you wish to work with actually exists.
• flush() - This method will write the contents of the buffer to the specified file, which is the file you've just opened. It is similar to the copy and paste from the clipboard action within Windows computers.
• getLength() - This method is used to tell you the length of the file, in bytes.
• getPosition() - This method is used to tell you the current position within the file you are working with.
• open() - This method is used to open the desired file and ready it for your changes.
• read() - This method reads the number of characters within a string.
• readByte() - This method reads the next character (byte) which is next within the file.
• readln() - This method reads the line of text (bytes) which follows the current position within the file.
• setPosition() - This method sets the position you will be working at within the file.
• stringToByte() - This method is used to convert the string passed as the parameter to the method into its byte code equivalent.
• write() - This method is used to write your text to the file which was opened, and which you are working with.
• writeByte() - This method is used to write binary data to a binary file which you have opened.
• writeln() - This method is used to write the text you desire to the file, and includes a carriage return character at the end of the text.

You can see the huge amount of functionality available to you for working with files on the server. While you'll use all of the above methods eventually, it is the open() method which you will use the most. This makes sense because you'll have to use it to open every file you work with. Because of this high amount of use, there are some properties of the open() method which I feel should be mentioned here. They're fairly simple and straightforward, and are as follows.

• a - This is used to open a file and ready it to be appended to. If the file doesn't exist, it is created. Only text files will be created, of any extension. A value of true is always returned.
• a+ - This is used to open a file and ready it to be read and appended to. If the file doesn't exist, it is created. Only text files will be created, of any extension. A value of true is always returned.
• r - This is used to open a file and ready it to be read. If the file doesn't exist, a value of false is returned. If it does exist, a value of true is returned.
• r+ - This is used to open a file and ready it to be read and written to. If the file doesn't exist, a value of false is returned. If it does exist, a value of true is returned. It should be noted that both the reading and writing of the file will begin at the beginning of the file.
• w - This is used to open a file and ready it to be written to. If the file doesn't exist, it is created. If the file already exists, it is overwritten. Only text files will be created, of any extension. A value of true is always returned.
• w+ - This is used to open a file and ready it to be read and written to. If the file doesn't exist, it is created. If the file already exists, it is overwritten. Only text files will be created, of any extension. A value of true is always returned.
• optionb - Using the b option with any of the above options specifies that a binary file is to be read, written, appended or created, according to the option given.

Thanks for joining us here at the JavaScript Chronicles. Swing by next week when we cover JavaScript and forms.

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