JavaScript And DHTML Cookbook [Electronic resources]

1.8 Using Special and Escaped Characters

NN 2, IE 3

1.8.1 Problem

You want to add low-order ASCII characters (tab, carriage return, etc.) to a string.

1.8.2 Solution

Use the escape sequences shown in Table 1-2 to represent the desired character. For example, to include an apostrophe inside a literal string, use \', as in:

var msg = "Welcome to Joe\'s Diner.";

1.8.3 Discussion

The core JavaScript language includes a feature common to most programming languages that lets you designate special characters. A special character is not one of the plain alphanumeric characters or punctuation symbols, but has a particular meaning with respect to whitespace in text. Common characters used these days include the tab, newline, and carriage return.

A special character begins with a backslash, followed by the character representing the code, such as \t for tab and \n for newline. The backslash is called an

escape character , instructing the interpreter to treat the next character as a special character. Table 1-2 shows the recognized escape sequence characters and their meanings. To include these characters in a string, include the backslash and special character inside the quoted string:

var confirmString = "You did not enter a response to the last " +
"question.\n\nSubmit form anyway?";

If you want to use one of these symbols between variables that contain string values, be sure the special character is quoted in the concatenation statement:

var myStr = lineText1 + "\n" + lineText2;

Special characters can be used to influence formatting of text in basic dialog boxes (from the alert( ), confirm( ), and prompt( ) methods) and textarea form controls.

Table 1-2 shows the recognized escaped characters and their meanings.

Note that to include a visible backslash character in a string, you must use a double backslash because a single one is treated as the invisible escape character. Use the escaped quote symbols to include single or double quotes inside a string.

While you can use an escaped character in tests for the existence of, say, line feed characters in a string, you have to exercise some care when doing so with the content of a textarea element. The problem accrues from a variety of implementations of how user-entered carriage returns are coded in the textarea's content. IE for Windows inserts two escaped characters (\r\n in that sequence) whenever a user presses the Enter key to make a newline in a textarea. But IE for Macintosh uses only the \r character. And Netscape 6 and later inserts \n for newlines. Navigator 4 is governed more by the operating system in which the browser runs: \r\n for Windows; \r for Macintosh; and \n for Unix. This wide variety in character combinations makes searches for user-typed line breaks difficult to perform accurately across browsers and operating systems.

Going the other waycreating a string for script insertion into a textarea valueis easier because modern browsers accommodate all symbols. Therefore, if you assign just \r or \n or the combination \r\n, all browsers interpret any one of them as a carriage return, and convert the escape character(s) to match their internal handling.

1.8.4 See Also

Recipe 1.1 for tips on concatenating stringstips that apply equally to escaped string characters.