JavaScript
Regular Expressions
A regular
expression is a sequence of characters that forms a search pattern.
The search
pattern can be used for text search and text replace operations.
What Is a
Regular Expression?
A regular
expression is a sequence of characters that forms a search pattern.
When you
search for data in a text, you can use this search pattern to describe what you
are searching for.
A regular
expression can be a single character, or a more complicated pattern.
Regular
expressions can be used to perform all types of text search and text replace
operations.
Syntax
/pattern/modifiers;
Example
var
patt = /Omegas1/i;
Example
explained:
/Omegas1/i is a regular expression.
Omegas1 is a pattern (to be used in a search).
i is a modifier (modifies the search to be
case-insensitive).
Using String
Methods
In
JavaScript, regular expressions are often used with the two string methods:
search() and replace().
The search()
method uses an expression to search for a match, and returns the position of
the match.
The
replace() method returns a modified string where the pattern is replaced.
Using String
search() With a Regular Expression
Example
Use a
regular expression to do a case-insensitive search for "Omegas1" in a
string:
var
str = "Visit Omegas1";
var
n = str.search(/Omegas1/i);
The result
in n will be:
6
»
Using String
search() With String
The search
method will also accept a string as search argument. The string argument will
be converted to a regular expression:
Example
Use a string
to do a search for "Omegas1" in a string:
var
str = "Visit Omegas1!";
var
n = str.search("Omegas1");
»
Use String
replace() With a Regular Expression
Example
Use a case
insensitive regular expression to replace Microsoft with Omegas1 in a string:
var
str = "Visit Microsoft!";
var
res = str.replace(/microsoft/i, "Omegas1");
The result
in res will be:
Visit Omegas1!
»
Using String
replace() With a String
The
replace() method will also accept a string as search argument:
var
str = "Visit Microsoft!";
var
res = str.replace("Microsoft", "Omegas1");
»
Did You
Notice?
Regular
expression arguments (instead of string arguments) can be used in the methods
above.
Regular
expressions can make your search much more powerful (case insensitive for
example).
Regular Expression
Modifiers
Modifiers
can be used to perform case-insensitive more global searches:
Modifier Description
i Perform case-insensitive matching
g Perform a global match (find all matches
rather than stopping after the first match)
m Perform multiline matching
Regular
Expression Patterns
Brackets are
used to find a range of characters:
Expression Description
[abc] Find any of the characters between the
brackets
[0-9] Find any of the digits between the brackets
(x|y) Find any of the alternatives separated with |
Metacharacters
are characters with a special meaning:
Metacharacter Description
\d Find a digit
\s Find a whitespace character
\b Find a match at the beginning or at the end of
a word
\uxxxx Find the Unicode character specified by
the hexadecimal number xxxx
Quantifiers
define quantities:
Quantifier Description
n+ Matches any string that contains at least one n
n* Matches any string that contains zero or more
occurrences of n
n? Matches any string that contains zero or one
occurrences of n
Using the
RegExp Object
In
JavaScript, the RegExp object is a regular expression object with predefined
properties and methods.
Using test()
The test()
method is a RegExp expression method.
It searches
a string for a pattern, and returns true or false, depending on the result.
The
following example searches a string for the character "e":
Example
var
patt = /e/;
patt.test("The
best things in life are free!");
Since there
is an "e" in the string, the output of the code above will be:
true
»
You don't
have to put the regular expression in a variable first. The two lines above can
be shortened to one:
/e/.test("The
best things in life are free!");
Using exec()
The exec()
method is a RegExp expression method.
It searches
a string for a specified pattern, and returns the found text.
If no match
is found, it returns null.
The
following example searches a string for the character "e":
Example
1
/e/.exec("The
best things in life are free!");
Since there
is an "e" in the string, the output of the code above will be:
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