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 way—creating a string for script insertion into a textarea value—is 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 strings—tips that apply equally to escaped string characters.