Special characters in regular expressions

Whether to ignore case while attempting a match in a string.

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.

The index at which to start the next match. A read/write integer property that specifies the index at which to start the next match.

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:

• If lastIndex is greater than the length of the string, regexp.test and regexp.exec fail, and lastIndex is set to 0.
• If 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.
• If 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.
• Otherwise, lastIndex is set to the next position following the most recent match.

For example, consider the following sequence of statements:

• re = /(hi)?/g Matches the empty string.
• re("hi") Returns ["hi", "hi"] with lastIndex equal to 2.
• re("hi") Returns [""], an empty array whose zeroth element is the match string. In this case, the empty string because lastIndex was 2 (and still is 2) and "hi" has length 2.

Whether or not to search in strings across multiple lines.

multiline is a property of an individual regular expression object..

The value of multiline is true if the "m" flag was used; otherwise, false. The "m" flag indicates that a multiline input string should be treated as multiple lines. For example, if "m" is used, "^" and "$" change from matching at only the start or end of the entire string to the start or end of any line within the string.

You cannot change this property directly.

The text of the pattern.

A read-only property that contains the text of the pattern, excluding the forward slashes.

source is a property of an individual regular expression object.

You cannot change this property directly.

Executes a search for a match in its string parameter.

If the match succeeds, the exec method returns an array and updates properties of the regular expression object. The returned array has the matched text as the first item, and then one item for each capturing parenthesis that matched containing the text that was captured. If the match fails, the exec method returns null.

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:

// Match one d followed by one or more b's followed by one d
// Remember matched b's and the following d
// Ignore case
var re = /d(b+)(d)/ig;
var result = re.exec("cdbBdbsbz");

The following table shows the results for this 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 (test will also advance the lastIndex property). For example, assume you have this script:

var myRe = /ab*\/g;
var str = "abbcdefabh";
var myArray;
while ((myArray = myRe.exec(str)) != null)
{
    var msg = "Found " + myArray[0] + ".  ";
    msg += "Next match starts at " + myRe.lastIndex;
print(msg);
}

This script displays the following text:

Found abb. Next match starts at 3
Found ab. Next match starts at 9

You can also use exec() without creating a RegExp object:

var matches = /(hello \S+)/.exec('This is a hello world!');
alert(matches[1]);

This will display an alert containing 'hello world!';

Parameters

• str : String

  The string against which to match the regular expression.

Returns

• Array

  Array of results or NULL.

Tests for a match in its string parameter.

When you want to know whether a pattern is found in a string use the test method (similar to the String.search method); for more information (but slower execution) use the exec method (similar to the String.match method). As with exec (or in combination with it), test called multiple times on the same global regular expression instance will advance past the previous match.

The following example prints a message which depends on the success of the test:

function testinput(re, str){
    if (re.test(str))
        midstring = " contains ";
    else
        midstring = " does not contain ";
    document.write (str + midstring + re.source);
}

Parameters

• str : String

  The string against which to match the regular expression.

Returns

• Boolean

  true if string contains any matches, otherwise returns false.

Returns a string representing the specified object. Overrides the Object.prototype.toString method.

The RegExp object overrides the toString method of the Object object; it does not inherit Object.toString. For RegExp objects, the toString method returns a string representation of the regular expression.

The following example displays the string value of a RegExp object:

myExp = new RegExp("a+b+c");
alert(myExp.toString());       // displays "/a+b+c/"

Returns

• String

  Regular expression as a string.