Platform Support
IE | Mozilla | Netscape | Opera | Safari | 4.0+ | 1.0+ | 4.0+ | 7.0+ | 1.0+ |
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Constructors
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RegExp Constructor([String pattern,] [String flags]) : RegExp
Creates a new instance of RegExp.
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RegExp([String pattern,] [String flags]) : RegExpCreates a new instance of RegExp. Parameters
Returns
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Properties
Property | Action | IE | Mozilla | Netscape | Opera | Safari |
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$n
: String
String corresponding to the (nth) expression of a match.
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Show Details | 4.0+ | 1.0+ | 4.0+ | 7.0+ | no |
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constructor
: Object
Specifies the function that creates the RegExp prototype.
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global
: Boolean
Whether or not the "g" flag is used with
the regular expression.
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ignoreCase
: Boolean
Whether or not the "i" flag is used with
the regular expression.
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Show Details | 5.5+ | 1.0+ | 4.0+ | 7.0+ | 1.0+ |
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index
: Number
Character position of the start of the first match.
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Show Details | 4.0+ | no | no | no | no |
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input
: String
String containing the most recently found regular expression match.
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Show Details | 4.0+ | 1.0+ | 4.0+ | no | no |
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lastIndex
: Number
A read/write integer property that specifies the index
at which to start the next match.
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Show Details | 4.0+ | 1.0+ | 4.0+ | 7.0+ | 1.0+ |
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lastMatch
: String
String containing the last characters of the last regular expression match.
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Show Details | 5.5+ | 1.0+ | 4.0+ | no | no |
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lastParen
: String
String containing the most recent parenthesized match.
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Show Details | 5.5+ | 1.0+ | 4.0+ | no | no |
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leftContext
: String
String containing the characters before the most recently found regular expression match.
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Show Details | 5.5+ | 1.0+ | 4.0+ | no | no |
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multiline
: Boolean
Whether or not the "m" (multiline) flag is used with the regular expression.
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Show Details | 5.5+ | 1.0+ | 4.0+ | no | 1.0+ |
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prototype
: Object
Reference to the RegExp prototype object.
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Show Details | 4.0+ | 1.0+ | 4.0+ | 7.0+ | 1.0+ |
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rightContext
: String
String containing the characters following the most recently found regular expression match.
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Show Details | 5.5+ | 1.0+ | 4.0+ | no | no |
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source
: String
A read-only property that contains the text of the
pattern, excluding the forward slashes.
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Show Details | 4.0+ | 1.0+ | 4.0+ | 7.0+ | 1.0+ |
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Functions
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compile(Object expr, Object flags) : RegExp
Creates a new regular expression by compiling the specified regular expression with the specified flags.
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Parameters
Returns
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exec(String regexp, String str) : Array
Executes the search for a match in a specified string.
Returns a result array.
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Parameters
Returns
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test(String regexp, String str) : Boolean
Executes the search for a match between a regular expression and a specified string.
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Parameters
Returns
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toSource() : String
Returns a string representing the source code of the object.
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Returns
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toString() : String
Returns a string representing the specified object.
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Returns
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Using the replace
method
The following script uses the replace
method to switch the words in the string. In the
replacement text, the script uses "$1
" and
"$2
" to indicate the results of the
corresponding matching parentheses in the regular
expression pattern.
var re = /(\w+)\s(\w+)/; var str = "John Smith"; var newstr = str.replace(re, "$2, $1"); document.write(newstr);
This displays "Smith, John".
Using input
In the following example,
RegExp.input
is
set by the Change event. In the getInfo
function, the exec
method uses the value of
RegExp.input
as its argument.
function getInfo() { var re = /(\w+)\s(\d+)/; var m = re.exec(); window.alert(m[0] + ", your age is " + m[2]); } Enter your first name and your age, and then press Enter. <form> <input type="text" name="NameAge" onchange="getInfo(this);"/> </form>
Remarks
When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary. For example, the following are equivalent:
re = new RegExp("\\w+") re = /\w+/
Special characters in regular expressions
Character | Meaning |
\ | For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally. For example, -or- For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally. For example, * is a special character that means
0 or more occurrences of the preceding character
should be matched; for example, |
^ | Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character. For example, |
$ | Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character. For example, |
* | Matches the preceding item 0 or more times. For example, |
+ | Matches the preceding item 1 or more times.
Equivalent to For example, |
? | Matches the preceding item 0 or 1 time. For example, If used immediately after any of the quantifiers
Also used in lookahead assertions, described
under |
. | (The decimal point) matches any single character except the newline character. For example, |
(x) | Matches 'x' and remembers the match. These are called capturing parentheses. For example, |
(?:x) | Matches 'x' but does not remember the match.
These are called non-capturing parentheses. The
matched substring can not be recalled from the
resulting array's elements |
x(?=y) | Matches 'x' only if 'x' is followed by 'y'. For
example, |
x(?!y) | Matches 'x' only if 'x' is not followed by 'y'.
For example,
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x|y | Matches either 'x' or 'y'. For example, |
{n} | Where For example, |
{n,} | Where For example, |
{n,m} | Where For example, |
[xyz] | A character set. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen. For example, |
[^xyz] | A negated or complemented character set. That is, it matches anything that is not enclosed in the brackets. You can specify a range of characters by using a hyphen. For example, |
[\b] | Matches a backspace. (Not to be confused with
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\b | Matches a word boundary, such as a space. (Not
to be confused with For example, |
\B | Matches a non-word boundary. For example,
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\cX | Where For example, |
\d | Matches a digit character. Equivalent to
For example, |
\D | Matches any non-digit character. Equivalent to
For example, |
\f | Matches a form-feed. |
\n | Matches a linefeed. |
\r | Matches a carriage return. |
\s | Matches
a single white space character,
including space, tab, form feed, line feed.
Equivalent to For example, |
\S | Matches a single character other than white
space. Equivalent to For example, |
\t | Matches a tab. |
\v | Matches a vertical tab. |
\w | Matches any alphanumeric character including the
underscore. Equivalent to
For example, |
\W | Matches any non-word character.
Equivalent to
For example, |
\n | Where For example, |
\0 | Matches a NUL character. Do not follow this with another digit. |
\xhh | Matches the character with the code hh (two hexadecimal digits) |
\uhhhh | Matches the character with code hhhh (four hexadecimal digits). |
The literal notation provides compilation of the regular expression when the expression is evaluated. Use literal notation when the regular expression will remain constant. For example, if you use literal notation to construct a regular expression used in a loop, the regular expression won't be recompiled on each iteration.
The constructor of the regular expression object, for
example, new RegExp("ab+c")
, provides
runtime compilation of the regular expression. Use the
constructor function when you know the regular expression
pattern will be changing, or you don't know the pattern
and are getting it from another source, such as user
input.
A separate predefined RegExp
object is
available in each window; that is, each separate thread
of JavaScript execution gets its own RegExp
object. Because each script runs to completion without
interruption in a thread, this assures that different
scripts do not overwrite values of the
RegExp
object.
Availability
JavaScript 1.2|JScript 3.0|ECMAScript v3