JavaScript String Methods Cheatsheet

Creating Strings

const s = "hello";
const t = 'world';
const u = `Hello, ${name}!`;         // Template literal
const m = `line 1
line 2`;                              // Multiline
String(123);                          // "123"
(42).toString(16);                    // "2a" (hex)

Searching

Method	Returns	Description
`includes(str, pos?)`	`boolean`	Contains substring
`startsWith(str, pos?)`	`boolean`	Starts with substring
`endsWith(str, len?)`	`boolean`	Ends with substring
`indexOf(str, pos?)`	Index or `-1`	First occurrence
`lastIndexOf(str, pos?)`	Index or `-1`	Last occurrence
`search(regex)`	Index or `-1`	Search with regex
`match(regex)`	Array or `null`	Match against regex
`matchAll(regex)`	Iterator	All matches (needs `g` flag)

"hello world".includes("world");      // true
"hello world".startsWith("hello");    // true
"hello world".indexOf("o");           // 4
"hello".search(/l+/);                 // 2
"aabba".match(/a/g);                  // ["a", "a", "a"]

Extracting

Method	Returns	Description
`slice(start, end?)`	String	Extract section (supports negative index)
`substring(start, end?)`	String	Extract section (no negative index)
`at(index)`	Character	Character at index (supports negative)
`charAt(index)`	Character	Character at index
`charCodeAt(index)`	Number	UTF-16 code unit
`codePointAt(index)`	Number	Unicode code point

"hello world".slice(0, 5);            // "hello"
"hello world".slice(-5);              // "world"
"hello".at(-1);                       // "o"

Transforming

Method	Returns	Description
`toUpperCase()`	String	All uppercase
`toLowerCase()`	String	All lowercase
`trim()`	String	Remove whitespace both ends
`trimStart()`	String	Remove leading whitespace
`trimEnd()`	String	Remove trailing whitespace
`padStart(len, fill?)`	String	Pad start to length
`padEnd(len, fill?)`	String	Pad end to length
`repeat(n)`	String	Repeat n times
`normalize(form?)`	String	Unicode normalization

"  hello  ".trim();                    // "hello"
"5".padStart(3, "0");                  // "005"
"ha".repeat(3);                        // "hahaha"

Replacing

Method	Returns	Description
`replace(search, replacement)`	String	Replace first match
`replaceAll(search, replacement)`	String	Replace all matches

"hello world".replace("world", "JS"); // "hello JS"
"aaa".replaceAll("a", "b");           // "bbb"
"abc 123".replace(/\d+/, "#");        // "abc #"

// With capture groups
"John Smith".replace(/(\w+) (\w+)/, "$2, $1"); // "Smith, John"

// With function
"hello".replace(/./g, c => c.toUpperCase()); // "HELLO"

Splitting & Joining

"a,b,c".split(",");                   // ["a", "b", "c"]
"a,b,c".split(",", 2);                // ["a", "b"] (limit)
"hello".split("");                     // ["h", "e", "l", "l", "o"]
["a", "b", "c"].join("-");            // "a-b-c"

Concatenating

"hello" + " " + "world";              // "hello world"
"hello".concat(" ", "world");          // "hello world"
`${a} ${b}`;                          // Template literal

Comparing

"a" < "b";                            // true (lexicographic)
"a".localeCompare("b");               // -1 (locale-aware)
"a".localeCompare("A", undefined, { sensitivity: "base" }); // 0

Raw Strings & Escape Sequences

Escape	Description
`\n`	Newline
`\t`	Tab
`\\`	Backslash
`\'`	Single quote
`\"`	Double quote
`\uXXXX`	Unicode character
`\u{XXXXX}`	Unicode code point

String.raw`hello\nworld`;             // "hello\\nworld" (no escape)

Iteration

for (const char of "hello") { /* ... */ }
[..."hello"];                          // ["h", "e", "l", "l", "o"]

Common Recipes

// Capitalize first letter
s.charAt(0).toUpperCase() + s.slice(1);

// Truncate with ellipsis
s.length > n ? s.slice(0, n) + "..." : s;

// Count occurrences
(s.match(/pattern/g) || []).length;

// Remove all whitespace
s.replace(/\s/g, "");

// Slug from title
title.toLowerCase().replace(/\s+/g, "-").replace(/[^\w-]/g, "");

// Check if numeric
!isNaN(s) && !isNaN(parseFloat(s));