JavaScript String Methods: The Ultimate Cheat Sheet

Strings are everywhere. Master these methods and write cleaner code.

Search & Find

const str = 'Hello, World! Welcome to JavaScript.';

// Check existence
str.includes('World');           // true
str.includes('world');           // false (case-sensitive)
str.startsWith('Hello');         // true
str.endsWith('JavaScript.');     // true

// Find position
str.indexOf('World');            // 7
str.indexOf('xyz');              // -1 (not found)
str.lastIndexOf('o');            // 22 (last occurrence)

// Regex search
str.search(/world/i);            // 7 (case-insensitive)
str.match(/[A-Z]\w+/g);         // ['Hello', 'World', 'Welcome', 'JavaScript']
str.matchAll(/\w+/g);           // Iterator of all matches with groups

Extract & Slice

const str = 'Hello, World!';

// Character at position
str[0];           // 'H'
str.charAt(0);    // 'H'
str.charCodeAt(0); // 72 (Unicode code point)
str.at(-1);       // '!' (negative index works!)

// Substring
str.slice(7, 12);    // 'World'
str.slice(-6);       // 'orld!'
str.substring(0, 5); // 'Hello'

// Split into array
'hello world'.split(' ');       // ['hello', 'world']
'a,b,c,d'.split(',');           // ['a', 'b', 'c', 'd']
'abc'.split('');                // ['a', 'b', 'c']
'hello world'.split(/\s+/);     // ['hello', 'world']

// Part of string
str.substring(0, 5);   // 'Hello'
str.substr(7, 5);      // 'World' (start, length) — DEPRECATED, use slice

Transform

// Case
'hello'.toUpperCase();    // 'HELLO'
'HELLO'.toLowerCase();    // 'hello'
'hello world'.toLocaleUpperCase(); // Locale-aware

// Trim whitespace
'  hello  '.trim();        // 'hello'
'  hello  '.trimStart();   // 'hello  '
'  hello  '.trimEnd();     // '  hello'

// Pad
'5'.padStart(3, '0');     // '005'
'abc'.padEnd(10, '.');    // 'abc.......'

// Repeat
'ha'.repeat(3);           // 'hahaha'
'-'.repeat(20);           // '--------------------'

// Replace
'hello world'.replace('world', 'JavaScript');  // 'hello JavaScript'
'aabbcc'.replace(/b/g, 'x');                  // 'aaxxcc' (global regex)
'aabbcc'.replaceAll('b', 'x');                 // 'aaxxcc' (no regex needed!)

// Normalize Unicode
'café'.normalize('NFC').length;  // 4 (composed)
'café'.normalize('NFD').length;  // 5 (decomposed: e + accent)

Template Literals — Advanced

const name = 'Alex';
const age = 30;

// Multi-line
const bio = `My name is ${name}
I am ${age} years old
I love JavaScript`;

// Expressions inside ${}
console.log(`${2 + 3}`);                    // '5'
console.log(`${name.toUpperCase()}`);        // 'ALEX'
console.log(`${['a', 'b', 'c'].join(', ')}`); // 'a, b, c'

// Tagged templates
function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i] ? `<mark>${values[i]}</mark>` : '';
    return result + str + value;
  }, '');
}

highlight`Hello ${name}, you are ${age}`; 
// 'Hello <mark>Alex</mark>, you are <mark>30</mark>'

Practical Patterns

Slug generation

function slugify(text) {
  return text
    .toLowerCase()
    .trim()
    .replace(/[^\w\s-]/g, '')  // Remove special chars
    .replace(/[\s_]+/g, '-')   // Spaces/underscores to hyphens
    .replace(/--+/g, '-')       // Multiple hyphens to single
    .replace(/^-+|-+$/g, '');   // Remove leading/trailing hyphens
}

slugify('Hello World! This is a Test'); // 'hello-world-this-is-a-test'
slugify('  My   Blog Post  ');          // 'my-blog-post'

Truncate with ellipsis

function truncate(str, maxLength = 100) {
  if (str.length <= maxLength) return str;
  return str.slice(0, maxLength).replace(/\s+\S*$/, '') + '...';
}

truncate('This is a very long string that needs to be truncated', 20);
// 'This is a very long...'

Capitalize

const capitalize = (str) => str.charAt(0).toUpperCase() + str.slice(1);
capitalize('hello'); // 'Hello'

const titleCase = (str) => str.replace(
  /\b\w/g, 
  char => char.toUpperCase()
);
titleCase('the quick brown fox'); // 'The Quick Brown Fox'

const camelCase = (str) => str
  .replace(/(?:^\w|[A-Z]|\b\w)/g, (word, index) => 
    index === 0 ? word.toLowerCase() : word.toUpperCase()
  )
  .replace(/[-_\s]+/g, '');
camelCase('hello-world test_case'); // 'helloWorldTestCase'

const kebabCase = (str) => str
  .replace(/([a-z])([A-Z])/g, '$1-$2')
  .replace(/[\s_]+/g, '-')
  .toLowerCase();
kebabCase('helloWorld TestCase'); // 'hello-world-test-case'

String to various types

// Safe number parsing
const toNumber = (str) => Number(str) || 0;
toNumber('42');     // 42
toNumber('abc');    // 0
toNumber('');       // 0
toNumber(null);     // 0

// Parse query string
const params = new URLSearchParams('?page=1&limit=20&sort=name');
params.get('page');   // '1'
params.get('limit');  // '20'
params.has('sort');   // true
params.toString();    // 'page=1&limit=20&sort=name'

// String to boolean
const toBool = (str) => ['true', '1', 'yes'].includes(String(str).toLowerCase());
toBool('true');   // true
toBool('false');  // false
toBool('1');      // true

// Is valid JSON string?
const isJSON = (str) => {
  try { JSON.parse(str); return true; } 
  catch { return false; }
};

Performance Tips

// String concatenation: + is fine for a few, join() for many
// Slow: repeated +
let s = '';
for (let i = 0; i < 10000; i++) s += i; // Creates new string each time!

// Fast: array join
const parts = [];
for (let i = 0; i < 10000; i++) parts.push(i);
parts.join(''); // Much faster

// Or use template literals (modern engines optimize well)

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What's your favorite string method?

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