JavaScript String Methods Every Developer Should Know in 2026

Strings are everywhere in JavaScript — parsing URLs, processing user input, building UI labels, talking to APIs. Yet a lot of developers reach for regex or manual loops when a built-in string method would do the job cleaner and faster.

This guide covers the string methods worth memorising in 2026, grouped by what you're trying to do.

Searching and Testing

includes()

'hello world'.includes('world') // true
'hello world'.includes('World') // false — case sensitive

Use this instead of indexOf() !== -1. Cleaner intent, same performance.

startsWith() / endsWith()

'https://example.com'.startsWith('https') // true
'report.csv'.endsWith('.csv')             // true

// With a position argument
'hello world'.startsWith('world', 6) // true — starts at index 6

Useful for file type checks, URL validation, and protocol detection.

indexOf() / lastIndexOf()

'banana'.indexOf('a')     // 1
'banana'.lastIndexOf('a') // 5
'banana'.indexOf('x')     // -1 (not found)

Still useful when you need the actual position, not just a boolean.

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Extracting Parts

slice(start, end)

'hello world'.slice(6)     // 'world'
'hello world'.slice(0, 5)  // 'hello'
'hello world'.slice(-5)    // 'world' — negative counts from end

The go-to for extracting substrings. end is exclusive (not included in result).

substring(start, end)

Works like slice but doesn't accept negative indices. Prefer slice in modern code.

at(index)

'hello'.at(0)   // 'h'
'hello'.at(-1)  // 'o' — last character
'hello'.at(-2)  // 'l'

Cleaner than str[str.length - 1] for accessing from the end.

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Transforming

toUpperCase() / toLowerCase()

'Hello World'.toUpperCase() // 'HELLO WORLD'
'Hello World'.toLowerCase() // 'hello world'

trim() / trimStart() / trimEnd()

'  hello world  '.trim()      // 'hello world'
'  hello world  '.trimStart() // 'hello world  '
'  hello world  '.trimEnd()   // '  hello world'

Always trim user input before comparison or storage.

replace() / replaceAll()

'foo bar foo'.replace('foo', 'baz')    // 'baz bar foo' — first match only
'foo bar foo'.replaceAll('foo', 'baz') // 'baz bar baz'

// With regex
'hello WORLD'.replace(/[A-Z]+/g, match => match.toLowerCase()) // 'hello world'

padStart() / padEnd()

'5'.padStart(3, '0')  // '005' — zero-pad numbers
'hi'.padEnd(10, '.')  // 'hi........'

Common for formatting IDs, timestamps, and table output.

repeat()

'ha'.repeat(3)  // 'hahaha'
'-'.repeat(40)  // '----------------------------------------'

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Splitting and Joining

split(separator)

'a,b,c'.split(',')        // ['a', 'b', 'c']
'hello'.split('')         // ['h', 'e', 'l', 'l', 'o']
'hello'.split('', 3)      // ['h', 'e', 'l'] — limit
'a  b  c'.split(/\s+/)   // ['a', 'b', 'c'] — regex separator

Pair with Array.join() to transform and reassemble:

'hello world'
  .split(' ')
  .map(word => word[0].toUpperCase() + word.slice(1))
  .join(' ')
// 'Hello World' — basic title case

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Matching with Regex

match() / matchAll()

'test 123 foo 456'.match(/\d+/g)     // ['123', '456']
'test 123 foo 456'.match(/\d+/)      // ['123', index: 5, ...]

// matchAll gives full match objects (requires /g flag)
const matches = [...'foo 123 bar 456'.matchAll(/(\w+)\s(\d+)/g)]
matches[0][1] // 'foo', matches[0][2] // '123'

search(regex)

'hello world'.search(/world/) // 6 (index of match)
'hello world'.search(/xyz/)   // -1

Like indexOf but accepts regex.

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Comparing

localeCompare()

['banana', 'Apple', 'cherry'].sort((a, b) => a.localeCompare(b))
// ['Apple', 'banana', 'cherry'] — case-insensitive sort

// Language-aware comparison
'é'.localeCompare('e', 'fr') // correctly handles accented characters

Don't use < or > for string sorting — they compare Unicode code points, not linguistic order.

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Template Literals (not a method, but worth including)

const name = 'world'
const greeting = `Hello, ${name}!`  // 'Hello, world!'

// Multiline
const html = `
  <div class="card">
    <h2>${title}</h2>
    <p>${description}</p>
  </div>
`

// Tagged templates (advanced)
const result = sql`SELECT * FROM users WHERE id = ${userId}`

Tagged templates are used in libraries like styled-components and graphql-tag — worth understanding even if you don't write your own.

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Quick Reference Table

Method	What it does
includes(s)	Returns true if string contains s
startsWith(s)	Returns true if string starts with s
endsWith(s)	Returns true if string ends with s
indexOf(s)	Position of first match, -1 if not found
slice(start, end)	Extract substring
at(i)	Character at index (supports negative)
toUpperCase()	All uppercase
toLowerCase()	All lowercase
trim()	Remove leading/trailing whitespace
replace(s, r)	Replace first match
replaceAll(s, r)	Replace all matches
padStart(n, c)	Pad to length n with char c
split(sep)	Split into array
match(rx)	Find matches
localeCompare(s)	Linguistically correct comparison

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Practical Example: Normalising User Input

Here's a common real-world task — taking raw user input and normalising it for storage:

function normaliseInput(raw) {
  return raw
    .trim()
    .toLowerCase()
    .replace(/\s+/g, ' ')      // collapse multiple spaces to one
    .replace(/[^a-z0-9 ]/g, '') // remove special characters
}

normaliseInput('  Hello   World!! ') // 'hello world'

And for slug generation (URL-friendly strings):

function toSlug(title) {
  return title
    .toLowerCase()
    .trim()
    .replace(/\s+/g, '-')
    .replace(/[^a-z0-9-]/g, '')
}

toSlug('Hello World: A Guide') // 'hello-world-a-guide'

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