JAVASCRIPT > les expressions régulières (regex)

SYNTAXE

/RegEx/flags;

REMPLACER

remplace la première occurrence trouvée :

 

chaine.replace( new RegExp(‘to‘,‘i’), ‘ta‘ );

ou

chaine.replace( /to/i, ‘ta‘ );

 

TESTER

var test = /to/.test(chaine);

 

renvoie true si l’occurence est trouvée, sinon renvoie false.

CHERCHER


var chaine = "Voici une phrase : toto";

var test = chaine.search(/to/i);

 

renvoie -1 si rien n’est trouvé, sinon, renvoie la position de la première occurrence trouvée (0 étant la première position).

 

 

RETOURNER


 

var test = /to/.exec("Une phrase avec toto");

 

Si une occurrence est trouvée, renvoie le résultat de la première occurrence trouvée, sinon renvoie null.

 

exemples :

 

var test = /to./.exec("to1 to2 to3″); →  to1

 

var test = /ti./.exec("t01 to2 to3"); →  null

 

 

 

Pour chercher la dernière occurrence :

bar(?!.*bar)

bar # Match bar

(?! # but only if it's not followed by...

.* # zero or more characters

bar # literal bar

) # end of lookahead

If your string may contain newline characters, use

bar(?![\s\S]*bar)

instead. [\s\S] matches any character, including newlines.

For example:

match = subject.match(/bar(?![\s\S]*bar)/);
if (match != null) {
    // matched text: match[0]
    // match start: match.index
}

You might also want to surround your search words (if they are indeed words composed of alphanumeric characters) with \b anchors to avoid partial matches.

\bbar\b(?![\s\S]*\bbar\b)

matches the solitary bar instead of the bar within foobar:

Don't match bar, do match bar, but not foobar!
  no match---^     match---^    no match---^

LES FLAGS

i Permet une application non sensible à la casse

replace( /to/i, ‘TO’ );

 

g Permet une application globale

replace( /to/g, ‘ta’ );
m Permet une application multiligne

replace( /to/m, ‘ta’ );

LES ENCADREMENTS (  ) ET [  ]

[abc] Un des caractères présents entre les crochets
[0-9] Un des caractères compris entre 0 et 9
(x|y) Un des schéma compris entre parenthèse et séparés par |

\d (digital)

\d Trouver une nombre

\b (mot)

\b Find a match at the beginning or at the end of a word

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

 

\s et \S (espaces)

\s Tout caractère espacé ( espace - tabulation \t - retour charriot \r - saut de ligne \n - tabulation verticale ).

\S Tout caractère non espacé ( espace - tabulation \t - retour charriot \r - saut de ligne \n - tabulation verticale ).

 

VAR = "Ceci est une phrase";
var patt1 = /\S/g;

 

Quelques RegEx

REMPLACER LES SAUTS DE LIGNES PAR DES <BR> :

 

replace( new RegExp(‘\r?\n’,'g’), ‘<br>’ );

---

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 "w3schools" in a string:

"highELE">var str = "highVAL">"Visit W3Schools";
"highELE">var n = str.search(/w3schools/i);

The result in n will be:

6

Try it Yourself »

---

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 "W3schools" in a string:

"highELE">var str = "highVAL">"Visit W3Schools!";
"highELE">var n = str.search("highVAL">"W3Schools");

Try it Yourself »

---

Use String replace() With a Regular Expression

Example

Use a case insensitive regular expression to replace Microsoft with W3Schools in a string:

"highELE">var str = "highVAL">"Visit Microsoft!";
"highELE">var res = str.replace(/microsoft/i, "highVAL">"W3Schools");

The result in res will be:

Visit W3Schools!

Try it Yourself »

Using String replace() With a String

The replace() method will also accept a string as search argument:

"highELE">var str = "highVAL">"Visit Microsoft!";
"highELE">var res = str.replace("highVAL">"Microsoft", "highVAL">"W3Schools");

Try it Yourself »

---

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

"highELE">var patt = /e/;
patt.test("highVAL">"The best things in life are free!");

Since there is an "e" in the string, the output of the code above will be:

true

Try it yourself »You don’t have to put the regular expression in a variable first. The two lines above can be shortened to one:

/e/.test("highVAL">"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("highVAL">"The best things in life are free!");

Since there is an "e" in the string, the output of the code above will be:

e

Try it yourself »

---

Complete RegExp Reference

For a complete reference, go to our Complete JavaScript RegExp Reference.

The reference contains descriptions and examples of all RegExp properties and methods.