RegExp
The RegExp object is used for matching text with a pattern
Defining RegExp
const re = /pattern/flags;
// Example
const re = /\w+\s/g;
or
const re = new RegExp("pattern", "flags");
// Example
const re = new RegExp("\\w+\\s", "g");
Note: flags are an integral part of a regular expression. They cannot be added or removed later.
| Flag | Description |
|---|---|
| d | Generate indices for substring matches. |
| g | Global search. |
| i | Case-insensitive search. |
| m | Multi-line search. |
| s | Allows . to match newline characters. |
| u | “unicode”; treat a pattern as a sequence of unicode code points. |
| y | Perform a “sticky” search that matches starting at the current position in the target string. See sticky. |
RegExp can be used with RegExp Methods and String Methods
RegExp methods
| Method | Description |
|---|---|
exec() |
Executes a search for a match in a string. It returns an array of information or null on a mismatch. more information (but slower execution) |
test() |
Tests for a match in a string. It returns true or false. Use this when you want to know whether a pattern is found in a string |
String methods
| Method | Description |
|---|---|
match() |
Returns an array containing all of the matches, including capturing groups, or null if no match is found. more information (but slower execution) |
matchAll() |
Returns an iterator containing all of the matches, including capturing groups. |
search() |
Tests for a match in a string and returns the index of the match, or -1 if the search fails. Use this to know whether a pattern is found in a string |
replace() |
Executes a search for a match in a string, and replaces the matched substring with a replacement substring. |
replaceAll() |
Executes a search for all matches in a string, and replaces the matched substrings with a replacement substring. |
split() |
Uses a regular expression or a fixed string to break a string into an array of substrings. |
Example for exec() and match()
const myRe = /d(b+)d/g;
const myArray = myRe.exec("cdbbdbdbddbbbbddbbbbbbdsbz");
// Output: ['dbbd', 'bb', index: 1, input: 'cdbbdbdbddbbbbddbbbbbbdsbz', groups: undefined]
// OR
const myArray = /d(b+)d/g.exec("cdbbdbdbddbbbbddbbbbbbdsbz");
// Output: ['dbbd', 'bb', index: 1, input: 'cdbbdbdbddbbbbddbbbbbbdsbz', groups: undefined]
// OR
"cdbbdbdbddbbbbddbbbbbbdsbz".match(/d(b+)d/g);
// Output: ['dbbd', 'dbd', 'dbbbbd', 'dbbbbbbd']
Now in above example exec returns 'dbbd' and 'bb' only as it only checks for a match, whereas match returns all the combinations hence it’s slower in execution
let myRegExp = /d(b+)d/g;
let myString = "0dbdbd";
let myArray = myRegExp.exec(myString);
console.log(`The value of lastIndex is ${myRegExp.lastIndex}`); // The value of lastIndex is 4
myArray = myRegExp.exec(myString);
console.log(`The value of lastIndex is ${myRegExp.lastIndex}`); // The value of lastIndex is 0
myArray = myRegExp.exec(myString);
console.log(`The value of lastIndex is ${myRegExp.lastIndex}`); // The value of lastIndex is 4
let myRegExp = /d(b+)d/g;
let myString = "0dbddbd";
let myArray = myRegExp.exec(myString);
myArray = myRegExp.exec(myString);
console.log(`The value of lastIndex is ${myRegExp.lastIndex}`); // The value of lastIndex is 4
myArray = myRegExp.exec(myString);
console.log(`The value of lastIndex is ${myRegExp.lastIndex}`); // The value of lastIndex is 7
myArray = myRegExp.exec(myString);
console.log(`The value of lastIndex is ${myRegExp.lastIndex}`); // The value of lastIndex is 0
const str = "fee fi fo fum";
const re = /\w+\s/g;
console.log(re.exec(str)); // ["fee ", index: 0, input: "fee fi fo fum"]
console.log(re.exec(str)); // ["fi ", index: 4, input: "fee fi fo fum"]
console.log(re.exec(str)); // ["fo ", index: 7, input: "fee fi fo fum"]
console.log(re.exec(str)); // null