HTML and CSS Reference
In-Depth Information
Table 17.6
Metacharacters and Metasymbols (continued)
Metacharacter/Met
asymbol
What It Matches
New with JavaScript 1.5
(?:x)
Matches
x
but does not remember the match. These are called
noncapturing parentheses. The matched substring cannot be recalled
from the resulting array's elements
[1]
, ...,
[n]
or from the predefined
RegExp
object's properties
$1, ..., $9
.
x(?=y)
Matches
x
only if
x
is followed by
y
. For example,
/Jack(?=Sprat)/
matches
Jack
only if it is followed by
Sprat
.
/Jack(?=Sprat|Frost)/
matches
Jack
only if it is followed by
Sprat
or
Frost
. However, neither
Sprat
nor
Frost
are part of the match results.
x(?!y)
Matches
x
only if
x
is not followed by
y
. For example,
/\d+(?!\.)/
matches a number only if it is not followed by a decimal point.
/\d+(?!\.)/.exec("3.141")
matches
141
but not
3.141
.
If you are searching for a particular character within a regular expression, you can use
the
dot
metacharacter to represent a single character, or a
character class
that matches
on one character from a set of characters. In addition to the dot and character class, Java-
Script has added some backslashed symbols (called metasymbols) to represent single
characters. See Table 17.7 for the single-character metacharacters, and Table 17.8 on
page 742 for a list of metasymbols.
Table 17.7
Single-Character and Single-Digit Metacharacters
Metacharacter
What It Matches
.
Matches any character except newline.
[a-z0-9_]
Matches any single character in set.
[^a-z0-9_]
Matches any single character
not
in set.
The dot metacharacter matches for any single character with the exception of the new-
line character. For example, the regular expression
/a.b/
is matched if the string contains
an
a
, followed by any one single character (except the
\n
), followed by
b
, whereas the
expression /.../ matches any string containing at least three characters.
