JavaScript Strings

String properties and methods

Template literals

Use backticks for interpolation and multi-line strings.

const name = "Eric";
const message = `Hello, ${name}!`;
 
const multi = `
  Line 1
  Line 2
`;

Accessing characters

.length

Returns the number of characters in the string.

"hello".length; // 5

.at()

Returns the character at an index, supporting negative indices.

"hello".at(1); // "e"
"hello".at(-1); // "o"

.charAt()

Returns the character at a specified index like .at(), but does not support negative indices.

"hello".charAt(0); // "h"

Searching

.includes()

Checks if a substring exists.

"hello world".includes("world"); // true
"hello world".includes("foo"); // false

.indexOf()

Returns the first index of a substring, or -1 if not found.

"hello world".indexOf("o"); // 4
"hello world".indexOf("z"); // -1

.lastIndexOf()

Returns the last index of a substring, or -1 if not found.

"hello world".lastIndexOf("o"); // 7
"hello world".lastIndexOf("z"); // -1

.startsWith() / .endsWith()

Check the beginning or end of a string.

"hello world".startsWith("hello"); // true
"hello world".endsWith("world"); // true

Extracting substrings

.slice()

Extracts a portion of the string. Supports negative indices.

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

.substring()

Extracts characters between two indices. Negative indices are treated as 0.

"hello world".substring(0, 5); // "hello"

.substr()

Extracts a substring from a start index and length. Supports negative start indices.

"hello world".substr(6, 5); // "world"
"hello world".substr(-5); // "world"

Splitting and joining

.split()

Splits the string into an array.

"foo,bar,baz".split(","); // ["foo", "bar", "baz"]
"hello".split(""); // ["h", "e", "l", "l", "o"]

.concat()

Joins two or more strings.

"Hello".concat(", ", "world"); // "Hello, world"

Replacing

.replace()

Replaces the first match. Replaces all matches with the global flag (g).

"abc".replace("a", "A"); // "Abc"
"abc abc".replace(/a/g, "A"); // "Abc Abc"

.replaceAll()

Replaces all matches.

"abc abc".replaceAll("a", "A"); // "Abc Abc"

Case and whitespace

.toUpperCase() / .toLowerCase()

Convert case.

"hello".toUpperCase(); // "HELLO"
"WORLD".toLowerCase(); // "world"

.trim()

Removes whitespace from both ends.

"  trim  ".trim(); // "trim"

.trimStart() / .trimEnd()

Remove whitespace from one end of the string.

"  trim  ".trimStart(); // "trim  "
"  trim  ".trimEnd(); // "  trim"

Padding and repeating

.padStart() / .padEnd()

Pad a string to a target length.

"5".padStart(3, "0"); // "005"
"5".padEnd(3, "0"); // "500"

.repeat()

Repeats the string.

"ha".repeat(3); // "hahaha"

Matching and searching with regex

.match()

Matches a string against a regular expression.

"hello 123".match(/\d+/); // ["123"]
"abc abc".match(/a/g); // ["a", "a"]

.search()

Returns the index of the first regex match, or -1 if not found.

"hello 123".search(/\d/); // 6
"hello".search(/z/); // -1

.localeCompare()

Compares two strings in locale order. Returns a negative number if the string comes first, zero if equal, positive if it comes after.

"a".localeCompare("b"); // -1
"b".localeCompare("a"); // 1
"a".localeCompare("a"); // 0