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In JavaScript, the RegExp object is a regular expression object with predefined properties and methods.
// literal notation
const re1 = /ab+c/i;
// constructor with string pattern as first argument
const re2 = new RegExp("ab+c", "i");
// constructor with regular expression literal as first argument
const re3 = new RegExp(/ab+c/, "i");
RegExp Object have the following methods.
| Method | Description |
|---|---|
| compile() | Compiles or re-compiles a regular expression (Deprecated) |
| exec() | Tests for a match in a string. Returns the first match |
| test() | Tests for a match in a string. Returns true or false |
| toString() | Returns the string value of the regular expression |
RegExp Object have the following properties.
| Property | Description |
|---|---|
| constructor | Returns the function that created the RegExp object's prototype |
| global | Checks whether the "g" modifier is set |
| ignoreCase | Checks whether the "i" modifier is set |
| lastIndex | Specifies the index at which to start the next match |
| multiline | Checks whether the "m" modifier is set |
| source | Returns the text of the RegExp pattern |
| dotAll | Checks whether the "s" modifier is set |
| flags | Returns the flags or modifiers of the RegExp pattern |
| hasIndices | Checks whether the "d" modifier is set |
| sticky | Checks whether the "y" modifier is set |
| unicode | Checks whether the "u" modifier is set |
| unicodeSets | Checks whether the "v" modifier is set |
compile() method is used to compile or recompile a regular expression with new source and flags after the RegExp object has already been created.
compile() method is deprecated and avoid using it.
const re = new RegExp("foo", "gi");
re.compile("new foo", "g");
exec() method tests for a match in a string. If it finds a match, it returns a result array, otherwise it returns null.
var str = "Javascript is an interesting scripting language";
var re1 = new RegExp("script", "g");
var re2 = new RegExp("pushing", "g");
re1.exec(str); // script
re2.exec(str); // null
test() method tests for a match in a string. If it finds a match, it returns true, otherwise it returns false.
var str = "Javascript is an interesting scripting language";
var re1 = new RegExp("script", "g");
var re2 = new RegExp("pushing", "g");
re1.test(str); // true
re2.test(str); // false
toString() method returns the string value of the regular expression.
var re1 = new RegExp("script", "g");
re1.toString(); // /script/g
var re2 = new RegExp("/", "g");
re2.toString(); // /\//g
constructor property returns the function that created the RegExp prototype.
var re = new RegExp("script", "g");
re.constructor; // function RegExp() { [native code] }
global property specifies whether or not the "g" modifier is set. This property returns true if the "g" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "g");
re1.global; // true
var re2 = new RegExp("script");
re2.global; // false
ignoreCase property specifies whether or not the "i" modifier is set. This property returns true if the "i" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "i");
re1.ignoreCase; // true
var re2 = new RegExp("script");
re2.ignoreCase; // false
lastIndex property specifies the index at which to start the next match. This property only works if the "g" modifier is set.
This property returns an integer that specifies the character position immediately after the last match found by exec( ) or test( ) methods.
exec( ) and test( ) reset lastIndex to 0 if they do not get a match.
var str = "Javascript is an interesting scripting language";
var re = new RegExp( "script", "g" );
re.lastIndex; // 0
re.test(str);
re.lastIndex; // 10
re.test(str);
re.lastIndex; // 35
re.test(str);
re.lastIndex; // 0
multiline property specifies whether or not the m modifier is set. This property returns true if the "m" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "m");
re1.multiline; // true
var re2 = new RegExp("script");
re2.multiline; // false
source property returns the text of the RegExp pattern.
var re = new RegExp("script", "m");
re.source; // script
dotAll property specifies whether or not the s modifier is set. This property returns true if the "s" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "s");
re1.dotAll; // true
var re2 = new RegExp("script");
re2.dotAll; // false
flags property returns the flags of this regular
var re1 = new RegExp("script", "g");
re1.flags; // g
var re2 = new RegExp("script", "yum");
re2.flags; // muy
var re3 = new RegExp("script");
re3.flags; //
hasIndices property specifies whether or not the d modifier is set. This property returns true if the "d" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "d");
re1.hasIndices; // true
var re2 = new RegExp("script");
re2.hasIndices; // false
sticky property specifies whether or not the y modifier is set. This property returns true if the "y" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "y");
re1.sticky; // true
var re2 = new RegExp("script");
re2.sticky; // false
unicode property specifies whether or not the u modifier is set. This property returns true if the "u" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "u");
re1.unicode; // true
var re2 = new RegExp("script");
re2.unicode; // false
unicodeSets property specifies whether or not the v modifier is set. This property returns true if the "v" modifier is set, otherwise it returns false.
var re1 = new RegExp("script", "v");
re1.unicodeSets; // true
var re2 = new RegExp("script");
re2.unicodeSets; // false
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