In addition to the properties of an individual regular expression object that you create using the RegExp
constructor function, the predefined RegExp
object has static properties that are set whenever any regular expression is used.
Core object | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
RegExp
constructor function. The literal format is used as follows:
/pattern/flagsThe constructor function is used as follows:
new RegExp("pattern", "flags")
pattern | The text of the regular expression. |
flags | (Optional) If specified, flags can have one of the following 3 values: |
Notice that the parameters to the literal format do not use quotation marks to indicate strings, while the parameters to the constructor function do use quotation marks. So the following expressions create the same regular expression:
/ab+c/i
new RegExp("ab+c", "i")
re = new RegExp("\\w+")Table 4.3 provides a complete list and description of the special characters that can be used in regular expressions.
re = /\w+/
Table 4.3 Special characters in regular expressions.
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. Once you have a defined regular expression, and if the regular expression is used throughout the script and may change, you can use the compile
method to compile a new regular expression for efficient reuse.
The predefined RegExp
object contains the static properties input
, multiline
, lastMatch
, lastParen
, leftContext
, rightContext
, and $1
through $9
. The input
and multiline
properties can be preset. The values for the other static properties are set after execution of the exec
and test
methods of an individual regular expression object, and after execution of the match
and replace
methods of String
.
RegExp
properties have both long and short (Perl-like) names. Both names always refer to the same value. Perl is the programming language from which JavaScript modeled its regular expressions.
| Compiles a regular expression object. |
| Executes a search for a match in its string parameter. |
| Tests for a match in its string parameter. |
replace
method to switch the words in the string. For the replacement text, the script uses the values of the $1
and $2
properties of the global RegExp
object. Note that the RegExp
object name is not be prepended to the $
properties when they are passed as the second argument to the replace
method. <SCRIPT LANGUAGE="JavaScript1.2">This displays "Smith, John".
re = /(\w+)\s(\w+)/;
str = "John Smith";
newstr=str.replace(re, "$2, $1");
document.write(newstr)
</SCRIPT>
Example 2. 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. Note that RegExp
is prepended to the $
properties.
<HTML>
<SCRIPT LANGUAGE="JavaScript1.2">
function getInfo() {
re = /(\w+)\s(\d+)/;
re.exec();
window.alert(RegExp.$1 + ", your age is " + RegExp.$2);
}
</SCRIPT>
Enter your first name and your age, and then press Enter.
<FORM>
<INPUT TYPE:"TEXT" NAME="NameAge" onChange="getInfo(this);">
</FORM>
</HTML>
Property of |
RegExp
|
Static, Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
input
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.input
.
The number of possible parenthesized substrings is unlimited, but the predefined RegExp
object can only hold the last nine. You can access all parenthesized substrings through the returned array's indexes.
These properties can be used in the replacement text for the String.replace
method. When used this way, do not prepend them with RegExp
. The example below illustrates this. When parentheses are not included in the regular expression, the script interprets $n
's literally (where n
is a positive integer).
replace
method to switch the words in the string. For the replacement text, the script uses the values of the $1
and $2
properties of the global RegExp
object. Note that the RegExp
object name is not be prepended to the $
properties when they are passed as the second argument to the replace
method. <SCRIPT LANGUAGE="JavaScript1.2">This displays "Smith, John".
re = /(\w+)\s(\w+)/;
str = "John Smith";
newstr=str.replace(re, "$2, $1");
document.write(newstr)
</SCRIPT>
input
.multiline
.lastMatch
.lastParen
.leftContext
.rightContext
."g"
flag is used with the regular expression.
Property of |
RegExp
|
Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
global
is a property of an individual regular expression object.
The value of global
is true
if the "g"
flag was used; otherwise, false
. The "g"
flag indicates that the regular expression should be tested against all possible matches in a string.
You cannot change this property directly. However, calling the compile
method changes the value of this property.
"i"
flag is used with the regular expression.
Property of |
RegExp
|
Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
ignoreCase
is a property of an individual regular expression object.
The value of ignoreCase
is true
if the "i"
flag was used; otherwise, false
. The "i"
flag indicates that case should be ignored while attempting a match in a string.
You cannot change this property directly. However, calling the compile
method changes the value of this property.
$_
is another name for the same property.
Property of |
RegExp
|
Static | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
input
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.input
.
If no string argument is provided to a regular expression's exec
or test
methods, and if RegExp.input
has a value, its value is used as the argument to that method.
TEXT
form element, input
is set to the value of the contained text. TEXTAREA
form element, input
is set to the value of the contained text. Note that multiline
is also set to true
so that the match can be executed over the multiple lines of text. SELECT
form element, input
is set to the value of the selected text. Link
object, input
is set to the value of the text between <A HREF=...>
and </A>
. input
property is cleared after the event handler completes.
Property of |
RegExp
|
Implemented in | Navigator 4.0, Netscape Server 3.0 |
lastIndex
is a property of an individual regular expression object.
This property is set only if the regular expression used the "g"
flag to indicate a global search. The following rules apply:
lastIndex
is greater than the length of the string, regexp.test
and regexp.exec
fail, and lastIndex
is set to 0
.lastIndex
is equal to the length of the string and if the regular expression matches the empty string, then the regular expression matches input starting at lastIndex
. lastIndex
is equal to the length of the string and if the regular expression does not match the empty string, then the regular expression mismatches input, and lastIndex
is reset to 0. lastIndex
is set to the next position following the most recent match.
$&
is another name for the same property.
Property of |
RegExp
|
Static, Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
lastMatch
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.lastMatch
.$+
is another name for the same property.
Property of |
RegExp
|
Static, Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
lastParen
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.lastParen
.$`
is another name for the same property.
Property of |
RegExp
|
Static, Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
leftContext
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.leftContext
.
Property of |
RegExp
|
Static | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
multiline
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.multiline
.
The value of multiline
is true
if multiple lines are searched, false
if searches must stop at line breaks.
$'
is another name for the same property.
Property of |
RegExp
|
Static, Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
rightContext
is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.rightContext
."g"
or "i"
flags.
Property of |
RegExp
|
Read-only | |
Implemented in | Navigator 4.0, Netscape Server 3.0 |
source
is a property of an individual regular expression object.
You cannot change this property directly. However, calling the compile
method changes the value of this property.
Method of |
RegExp
|
Implemented in | Navigator 4.0, Netscape Server 3.0 |
regexp.compile(pattern, flags)
compile
method to compile a regular expression created with the RegExp
constructor function. This forces compilation of the regular expression once only which means the regular expression isn't compiled each time it is encountered. Use the compile
method when you know the regular expression will remain constant (after getting its pattern) and will be used repeatedly throughout the script.
You can also use the compile
method to change the regular expression during execution. For example, if the regular expression changes, you can use the compile
method to recompile the object for more efficient repeated use.
Calling this method changes the value of the regular expression's source
, global
, and ignoreCase
properties.
Method of |
RegExp
|
Implemented in | Navigator 4.0, Netscape Server 3.0 |
regexp.exec(str)
regexp(str)
exec
method call be called either directly, (with regexp.exec(str)
) or indirectly (with regexp(str)
).
If you are executing a match simply to find true
or false
, use the test
method or the String
search
method.
Consider the following example:
<SCRIPT LANGUAGE="JavaScript1.2">The following table shows the results for this script:
//Match one d followed by one or more b's followed by one d
//Remember matched b's and the following d
//Ignore case
myRe=/d(b+)(d)/ig;
myArray = myRe.exec("cdbBdbsbz");
</SCRIPT>
If your regular expression uses the "g"
flag, you can use the exec
method multiple times to find successive matches in the same string. When you do so, the search starts at the substring of str
specified by the regular expression's lastIndex
property. For example, assume you have this script:
<SCRIPT LANGUAGE="JavaScript1.2">This script displays the following text:
myRe=/ab*/g;
str = "abbcdefabh"
myArray = myRe.exec(str);
document.writeln("Found " + myArray[0] +
". Next match starts at " + myRe.lastIndex)
mySecondArray = myRe.exec(str);
document.writeln("Found " + mySecondArray[0] +
". Next match starts at " + myRe.lastIndex)
</SCRIPT>
Found abb. Next match starts at 3
Found ab. Next match starts at 9
This script assumes that first names of registered party attendees are preloaded into the array A, perhaps by gathering them from a party database.
<HTML>
<SCRIPT LANGUAGE="JavaScript1.2">
A = ["Frank", "Emily", "Jane", "Harry", "Nick", "Beth", "Rick",
"Terrence", "Carol", "Ann", "Terry", "Frank", "Alice", "Rick",
"Bill", "Tom", "Fiona", "Jane", "William", "Joan", "Beth"]
function lookup() {
firstName = /\w+/i();
if (!firstName)
window.alert (RegExp.input + " isn't a name!");
else {
count = 0;
for (i=0; i<A.length; i++)
if (firstName[0].toLowerCase() == A[i].toLowerCase()) count++;
if (count ==1)
midstring = " other has ";
else
midstring = " others have ";
window.alert ("Thanks, " + count + midstring + "the same name!")
}
}
</SCRIPT>
Enter your first name and then press Enter.
<FORM> <INPUT TYPE:"TEXT" NAME="FirstName" onChange="lookup(this);"> </FORM>
</HTML>
true
or false
.
Method of |
RegExp
|
Implemented in | Navigator 4.0, Netscape Server 3.0 |
regexp.test(str)
test
method (similar to the String.search
method); for more information (but slower execution) use the exec
method (similar to the String.match
method). function testinput(re, str){
if (re.test(str))
midstring = " contains ";
else
midstring = " does not contain ";
document.write (str + midstring + re.source);
}
Last Updated: 10/31/97 12:30:31