JavaScript And DHTML Cookbook [Electronic resources] نسخه متنی

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.