JavaScript String Methods: The Ultimate Cheat Sheet

Strings are everywhere. Master these methods and you'll write cleaner code.

Search & Check

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

// Includes (ES6+ — use this!)
str.includes('World');        // true
str.includes('world');         // false (case-sensitive)
str.includes('Python');        // false

// Starts with / ends with
str.startsWith('Hello');       // true
str.startsWith('World', 7);    // true (from index 7)
str.endsWith('Script.');       // true
str.endsWith('.');             // true

// Index of first/last occurrence
str.indexOf('o');              // 4 (first 'o')
str.indexOf('o', 5);          // 8 (first 'o' after index 5)
str.lastIndexOf('o');          // 22 (last 'o')
str.indexOf('xyz');            // -1 (not found)

// Match with regex
str.match(/o/g);               // ['o', 'o', 'o'] — all matches
str.match(/javascript/i);      // ['JavaScript'] — case insensitive

Extract & Slice

const str = 'JavaScript is awesome';

// charAt — single character
str.charAt(0);                 // "J"
str[str.length - 1];           // "e" (last character)

// slice — extract portion (negative = from end)
str.slice(0, 10);              // "JavaScript"
str.slice(11);                 // "is awesome"
str.slice(-7);                 // "awesome"
str.slice(0, -8);              // "JavaScript is"

// substring — similar to slice but no negative indices
str.substring(0, 10);          // "JavaScript"

// split — string to array
'a,b,c,d'.split(',');          // ['a', 'b', 'c', 'd']
'hello world'.split(' ');       // ['hello', 'world']
'2026-05-16'.split('-');        // ['2026', '05', '16']
''.split(',');                  // [''] (empty array with one element)

// match + groups for extraction
const url = 'https://example.com/path?q=1';
url.match(/^https?:\/\/([^\/]+)/)?.[1];  // "example.com"

Transform

// Case conversion
'hello'.toUpperCase();          // "HELLO"
'HELLO'.toLowerCase();          // "hello"

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

// Replace
'hello world'.replace('world', 'universe');
// "hello universe"

'aaa bbb aaa'.replace('a', 'x');
// "xaa bbb aaa" (only first occurrence!)

'aaa bbb aaa'.replaceAll('a', 'x');
// "xxx bbb xxx" (all occurrences!)

// Replace with regex
'hello123world456'.replace(/\d+/g, '-');
// "hello-world-"

// Replace with function
'price: $100, tax: $15'.replace(/\$(\d+)/g, (_, num) => {
  return `$${Number(num) * 1.1}`; // Add 10% tax
});
// "price: $110, tax: $16.5"

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

// Pad
'5'.padStart(3, '0');          // "005"
'42'.padEnd(5, '.');           // "42..."
'abc'.padStart(10, '-');       // "-------abc"

Convert Types

// String → Number
Number('42');                   // 42
parseInt('42px', 10);          // 42 (stops at non-digit)
parseFloat('3.14rem');         // 3.14
+'100';                         // 100 (unary plus)
'100' * 1;                     // 100

// Number → String
String(42);                    // "42"
(42).toString();                // "42"
'' + 42;                       // "42"
42 + '';                        // "42"

// Boolean → String
String(true);                   // "true"
String(false);                  // "false"

// Anything → JSON string
JSON.stringify({ a: 1 });       // '{"a": 1}'
JSON.stringify({ a: 1 }, null, 2);
// {
//   "a": 1
// }

Template Literals (ES6+)

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

// Basic interpolation
`My name is ${name} and I am ${age} years old.`;
// "My name is Alex and I am 30 years old."

// Expressions in templates
`Next year I'll be ${age + 1}.`;
// "Next year I'll be 31."

// Multi-line strings
const html = `
  <div class="card">
    <h2>${name}</h2>
    <p>Age: ${age}</p>
  </div>
`;

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

highlight`User ${name} has ${age} items`;
// "User <mark>Alex</mark> has <mark>30</mark> items"

Unicode & Internationalization

// Emoji length (surprise! 😱)
'👨‍👩‍👧‍👦'.length;              // 11 (not 1!) — it's multiple code points
[...'👨‍👩‍👧‍👦'].length;        // 1 (spread into array of graphemes)

// Code points
'A'.codePointAt(0);            // 65
String.fromCodePoint(9733);     // "★"

// Locale-aware operations
'café'.normalize('NFD');        // Decomposed accents (for accent-insensitive search)
'I'.localeCompare('i');         // 0 (locale-aware comparison)

// Intl APIs
new Intl.NumberFormat('en-US').format(1234567.89);
// "1,234,567.89"

new Intl.NumberFormat('de-DE').format(1234567.89);
// "1.234.567,89"

new Intl.DateTimeFormat('en-US', { dateStyle: 'full' }).format(new Date());
// "Friday, May 16, 2026"

Practical Patterns

Slugify URL

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

slugify('Hello World! How Are You?');
// "hello-world-how-are-you"

Truncate Text

function truncate(str, maxLength, suffix = '...') {
  if (str.length <= maxLength) return str;
  return str.slice(0, maxLength - suffix.length) + suffix;
}

truncate('This is a very long sentence that should be truncated.', 20);
// "This is a very lo..."

Title Case

function titleCase(str) {
  return str.toLowerCase().replace(
    /\b\w/g,
    char => char.toUpperCase()
  );
}

titleCase('hello WORLD from javascript');
// "Hello World From Javascript"

Camel Case ↔ Snake Case

function snakeToCamel(str) {
  return str.replace(/_([a-z])/g, (_, letter) => letter.toUpperCase());
}
snakeToCamel('my_variable_name'); // "myVariableName"

function camelToSnake(str) {
  return str.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`);
}
camelToSnake('myVariableName'); // "my_variable_name"

Extract Numbers from String

function extractNumbers(str) {
  return str.match(/\d+(\.\d+)?/g) || [];
}

extractNumbers('Order #12345: $99.99 shipping');
// ['12345', '99.99']

Quick Reference

Method	Returns	Example
includes()	boolean	'hi'.includes('i') → true
startsWith()	boolean	'hi'.startsWith('h') → true
endsWith()	boolean	'hi'.endsWith('i') → true
indexOf()	number or -1	'hi'.indexOf('i') → 1
slice(start, end)	string	'hello'.slice(1,3) → 'el'
split(sep)	array	'a,b'.split(',') → ['a','b']
trim()	string	' x '.trim() → 'x'
toUpperCase()	string	'hi'.toUpperCase() → 'HI'
toLowerCase()	string	'HI'.toLowerCase() → 'hi'
replace(old, new)	string	First occurrence only
replaceAll(old, new)	string	All occurrences
repeat(n)	string	'x'.repeat(3) → 'xxx'
padStart(len, char)	string	'5'.padStart(3,'0') → '005'
match(regex)	array or null	Regex matches
charCodeAt(i)	number	ASCII/Unicode code

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