In this article, we learn about strings and their methods

What is String?

a string is a sequence of characters enclosed in single quotes (''), double quotes ("") or backticks (``).

Strings are immutable, meaning their values cannot be changed once created

Here are some commonly used string methods:

slice()

The slice() method extracts a part of a string and returns it as a new string, without modifying the original string.

Syntax

slice(indexStart)
slice(indexStart, indexEnd)

const str = 'The quick brown fox jumps over the lazy dog.';

console.log(str.slice(31));
// Expected output: "the lazy dog."

console.log(str.slice(4, 19));
// Expected output: "quick brown fox"

console.log(str.slice(-4));
// Expected output: "dog."

console.log(str.slice(-9, -5));
// Expected output: "lazy"

substring()

The substring() method returns the part of the string from the start index up to and excluding the end index.

Syntax

substring(indexStart)
substring(indexStart, indexEnd)

const str = 'Mozilla';

console.log(str.substring(1, 3));
// Expected output: "oz"

console.log(str.substring(2));
// Expected output: "zilla"

trim()

The trim() method removes whitespace from both ends of a string and returns a new string, without modifying the original string.

Syntax

trim()

const greeting = ' Hello world! ';

console.log(greeting); // Expected output: " Hello world! ";

console.log(greeting.trim()); // Expected output: "Hello world!";

trimEnd()

The trimEnd() method removes whitespace from the end of a string and returns a new string, without modifying the original string.

Syntax

trimEnd()

const greeting = '   Hello world!   ';

console.log(greeting);
// Expected output: "   Hello world!   ";

console.log(greeting.trimEnd());
// Expected output: "   Hello world!";

trimStart()

The trimStart() method removes whitespace from the beginning of a string and returns a new string, without modifying the original string.

trimStart()

const greeting = '   Hello world!   ';

console.log(greeting);
// Expected output: "   Hello world!   ";

console.log(greeting.trimStart());
// Expected output: "Hello world!   ";

toLowerCase()

The toLowerCase() method returns the calling string value converted to lower case

Syntax

toLowerCase()

const sentence = 'The quick brown fox jumps over the lazy dog.';

console.log(sentence.toLowerCase());
// Expected output: "the quick brown fox jumps over the lazy dog."

toUpperCase()

The toUpperCase() method returns the calling string value converted to uppercase

Syntax

toUpperCase()

const sentence = 'The quick brown fox jumps over the lazy dog.';

console.log(sentence.toUpperCase());
// Expected output: "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG."

split()

The split() method splits a string into an array of substrings based on a specified delimiter.

Syntax

split(separator)
split(separator, limit)

const str = 'The quick brown fox jumps over the lazy dog.';

const words = str.split(' ');
console.log(words[3]);
// Expected output: "fox"

const chars = str.split('');
console.log(chars[8]);
// Expected output: "k"

const strCopy = str.split();
console.log(strCopy);
// Expected output: Array ["The quick brown fox jumps over the lazy dog."]

startsWith()

The startsWith() method determines whether a string begins with the characters of a specified string, returning true or false as appropriate.

Syntax

startsWith(searchString)
startsWith(searchString, position)

const str1 = 'Saturday night plans';

console.log(str1.startsWith('Sat'));
// Expected output: true

console.log(str1.startsWith('Sat', 3));
// Expected output: false

search()

The search() method executes a search for a match between a regular expression and this String object.

Syntax

search(regexp)

const paragraph = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

// Any character that is not a word character or whitespace
const regex = /[^\w\s]/g;

console.log(paragraph.search(regex));
// Expected output: 43

console.log(paragraph[paragraph.search(regex)]);
// Expected output: "."

replace()

The replace() method returns a new string with one, some, or all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function called for each match. If pattern is a string, only the first occurrence will be replaced. The original string is left unchanged.

Syntax

replace(pattern, replacement)

const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';

console.log(p.replace('dog', 'monkey')); // Expected output: "The quick brown fox jumps over the lazy monkey. If the dog reacted, was it really lazy?"

const regex = /Dog/i; console.log(p.replace(regex, 'ferret')); // Expected output: "The quick brown fox jumps over the lazy ferret. If the dog reacted, was it really lazy?"

replaceAll()

The replaceAll() method returns a new string with all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match. The original string is left unchanged.

Syntax

replaceAll(pattern, replacement)

const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';

console.log(p.replaceAll('dog', 'monkey'));
// Expected output: "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?"


// Global flag required when calling replaceAll with regex
const regex = /Dog/ig;
console.log(p.replaceAll(regex, 'ferret'));
// Expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"

padStart()

The padStart() method pads the current string with another string (multiple times, if needed) until the resulting string reaches the given length. The padding is applied from the start of the current string.

Syntax

padStart(targetLength)
padStart(targetLength, padString)

const str1 = '5';

console.log(str1.padStart(2, '0'));
// Expected output: "05"

const fullNumber = '2034399002125581';
const last4Digits = fullNumber.slice(-4);
const maskedNumber = last4Digits.padStart(fullNumber.length, '*');

console.log(maskedNumber);
// Expected output: "************5581"

padEnd()

The padEnd() method pads the current string with a given string (repeated, if needed) so that the resulting string reaches a given length. The padding is applied from the end of the current string.

Syntax

padEnd(targetLength)
padEnd(targetLength, padString)

const str1 = 'Breaded Mushrooms';

console.log(str1.padEnd(25, '.'));
// Expected output: "Breaded Mushrooms........"

const str2 = '200';

console.log(str2.padEnd(5));
// Expected output: "200  "

match()

The match() method retrieves the result of matching a string against a regular expression.

Syntax

match(regexp)

const paragraph = 'The quick brown fox jumps over the lazy dog. It barked.';
const regex = /[A-Z]/g;
const found = paragraph.match(regex);

console.log(found);
// Expected output: Array ["T", "I"]

matchAll()

The matchAll() method returns an iterator of all results matching a string against a regular expression, including capturing groups.

Syntax

matchAll(regexp)

const regexp = /t(e)(st(\d?))/g;
const str = 'test1test2';

const array = [...str.matchAll(regexp)];

console.log(array[0]);
// Expected output: Array ["test1", "e", "st1", "1"]

console.log(array[1]);
// Expected output: Array ["test2", "e", "st2", "2"]

includes()

The includes() method performs a case-sensitive search to determine whether one string may be found within another string, returning true or false as appropriate.

Syntax

includes(searchString)
includes(searchString, position)

const sentence = 'The quick brown fox jumps over the lazy dog.';

const word = 'fox';

console.log(`The word "${word}" ${sentence.includes(word) ? 'is' : 'is not'} in the sentence`);
// Expected output: "The word "fox" is in the sentence"

indexOf()

The indexOf() method of String values searches this string and returns the index of the first occurrence of the specified substring. It takes an optional starting position and returns the first occurrence of the specified substring at an index greater than or equal to the specified number.

Syntax

indexOf(searchString)
indexOf(searchString, position)

const paragraph = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

const searchTerm = 'dog';
const indexOfFirst = paragraph.indexOf(searchTerm);

console.log(`The index of the first "${searchTerm}" from the beginning is ${indexOfFirst}`);
// Expected output: "The index of the first "dog" from the beginning is 40"

console.log(`The index of the 2nd "${searchTerm}" is ${paragraph.indexOf(searchTerm, (indexOfFirst + 1))}`);
// Expected output: "The index of the 2nd "dog" is 52"

charAt()

The charAt() method of String values returns a new string consisting of the single UTF-16 code unit located at the specified offset into the string.

Syntax

charAt(index)

const sentence = 'The quick brown fox jumps over the lazy dog.';

const index = 4;

console.log(`The character at index ${index} is ${sentence.charAt(index)}`);
// Expected output: "The character at index 4 is q"

concat()

The concat() method concatenates the string arguments to the calling string and returns a new string.

Syntax

concat(str1)
concat(str1, str2)

const str1 = 'Hello';
const str2 = 'World';

console.log(str1.concat(' ', str2));
// Expected output: "Hello World"

console.log(str2.concat(', ', str1));
// Expected output: "World, Hello"

endsWith()

The endsWith() method determines whether a string ends with the characters of a specified string, returning true or false as appropriate.

Syntax

endsWith(searchString)
endsWith(searchString, endPosition)

const str1 = 'Cats are the best!';

console.log(str1.endsWith('best!'));
// Expected output: true

console.log(str1.endsWith('best', 17));
// Expected output: true

const str2 = 'Is this a question?';

console.log(str2.endsWith('question'));
// Expected output: false

lastIndexOf()

The lastIndexOf() method of String values searches this string and returns the index of the last occurrence of the specified substring. It takes an optional starting position and returns the last occurrence of the specified substring at an index less than or equal to the specified number.

Syntax

lastIndexOf(searchString)
lastIndexOf(searchString, position)

const paragraph = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

const searchTerm = 'dog';

console.log(`The index of the first "${searchTerm}" from the end is ${paragraph.lastIndexOf(searchTerm)}`);
// Expected output: "The index of the first "dog" from the end is 52"