JavaScript String Methods & Operations - Complete Guide

1let str = "Hello";
2// Indices:  01234
3          
4// Access characters using index
5console.log(str[0]);     // "H"
6console.log(str[4]);     // "o"
7console.log(str[-1]);    // undefined (use at() for negative indices)
8console.log(str.at(-1)); // "o" (last character)

1let str = "JavaScript";
2
3// Different ways to access characters
4console.log(str[0]);        // "J"
5console.log(str.charAt(0)); // "J"
6console.log(str.at(0));     // "J"
7
8// Out of range behavior
9console.log(str[20]);        // undefined
10console.log(str.charAt(20)); // "" (empty string)
11console.log(str.at(-1));     // "t" (last character)
12console.log(str.at(-2));     // "p" (second to last)

1let str = "Hello";
2
3// Immutability
4str[0] = "h";         // No effect
5console.log(str);     // Still "Hello"
6
7// Case sensitivity
8console.log("Hello" === "hello"); // false
9
10// Unicode support
11let text = "Hello 👋 World 🌍";
12console.log(text.length);    // Length includes emoji characters
13console.log(text[6]);        // "👋" (emoji is a single character)

1let str = "Hello";
2console.log(str.length); // 5
3
4let empty = "";
5console.log(empty.length); // 0

1let str = "Hello";
2console.log(str.at(0));  // H
3console.log(str.at(-1)); // o (last character)
4console.log(str.at(-2)); // l (second to last)

1let str = "Hello World";
2console.log(str.indexOf("World")); // 6
3console.log(str.indexOf("world")); // -1 (case sensitive)
4console.log(str.indexOf("o", 5));  // 7 (starts search from index 5)

1let str = "Hello World";
2console.log(str.slice(0, 5));  // "Hello"
3console.log(str.slice(6));     // "World"
4console.log(str.slice(-5));    // "World"
5console.log(str.slice(-6, -1)); // "Worl"

1let str = "Hello World";
2console.log(str.replace("World", "JavaScript")); // "Hello JavaScript"
3console.log(str.replace("o", "0")); // "Hell0 World"

1let str = "ha ha ha";
2console.log(str.replaceAll("ha", "he")); // "he he he"
3console.log(str.replaceAll("a", "o")); // "ho ho ho"

1let str = "Hello";
2console.log(str.charAt(0));  // "H"
3console.log(str.charAt(4));  // "o"
4console.log(str.charAt(10)); // "" (empty string)

1let str = "Hello";
2console.log(str.charCodeAt(0)); // 72 (Unicode for 'H')
3console.log(str.charCodeAt(1)); // 101 (Unicode for 'e')
4console.log("ABC".charCodeAt(0)); // 65 (Unicode for 'A')

1let str = "Hello World, Hello JavaScript";
2console.log(str.lastIndexOf("Hello")); // 13
3console.log(str.lastIndexOf("Hello", 12)); // 0
4console.log(str.lastIndexOf("Python")); // -1 (not found)

1let str = "Hello World";
2console.log(str.includes("World")); // true
3console.log(str.includes("world")); // false (case sensitive)
4console.log(str.includes("Hello", 1)); // false (starts search from index 1)

1let str = "Hello World";
2console.log(str.startsWith("Hello")); // true
3console.log(str.startsWith("World")); // false
4console.log(str.startsWith("World", 6)); // true (starts check from index 6)

1let str = "Hello World";
2console.log(str.endsWith("World")); // true
3console.log(str.endsWith("Hello")); // false
4console.log(str.endsWith("Hello", 5)); // true (checks only first 5 characters)

1let str = "Hello World";
2console.log(str.toUpperCase()); // HELLO WORLD
3console.log(str.toLowerCase()); // hello world
4console.log("JavaScript".toLowerCase()); // javascript

1let str = "   Hello World   ";
2console.log(str.trim());      // "Hello World"
3console.log(str.trimStart()); // "Hello World   "
4console.log(str.trimEnd());   // "   Hello World"

1let str1 = "Hello";
2let str2 = "World";
3console.log(str1.concat(" ", str2)); // "Hello World"
4console.log("".concat(1, 2, 3));     // "123"
5console.log(str1.concat(", ", str2, "!")); // "Hello, World!"

1let str = "Hello World";
2console.log(str.substring(0, 5));  // "Hello"
3console.log(str.substring(6));     // "World"
4console.log(str.substring(6, 3));  // "llo" (swaps if start > end)
5console.log(str.substring(-3));    // "Hello World" (negative becomes 0)

1// Split string into words
2let str = "Hello World JavaScript";
3console.log(str.split(" ")); // ["Hello", "World", "JavaScript"]
4
5// Split with limit
6console.log(str.split(" ", 2)); // ["Hello", "World"]
7
8// Split into characters
9let text = "Hello";
10console.log(text.split("")); // ["H", "e", "l", "l", "o"]
11
12// Split CSV data
13let data = "John,Doe,25,Developer";
14console.log(data.split(",")); // ["John", "Doe", "25", "Developer"]

1let words = ["Hello", "World", "JavaScript"];
2console.log(words.join(" ")); // "Hello World JavaScript"
3
4// Join with different separators
5let items = ["apple", "banana", "orange"];
6console.log(items.join(", ")); // "apple, banana, orange"
7console.log(items.join("-")); // "apple-banana-orange"
8
9// Join without separator
10let chars = ["H", "e", "l", "l", "o"];
11console.log(chars.join("")); // "Hello"

1let str = "The rain in SPAIN stays mainly in the plain";
2
3// Regex Flags:
4// g (global) - Find all matches rather than stopping after first match
5// i (case insensitive) - Case doesn't matter when matching
6// m (multiline) - ^ and $ match start/end of each line
7// s (dotAll) - Dot (.) matches newline characters
8// y (sticky) - Matches only from lastIndex
9// u (unicode) - Enable unicode features
10
11// Using g flag to find all matches
12console.log(str.match(/ain/g)); // ["ain", "ain", "ain"]
13
14// Using i flag for case-insensitive search
15console.log(str.match(/spain/i)); // ["SPAIN"]
16
17// Using multiple flags (g and i)
18console.log(str.match(/the/gi)); // ["The", "the"]
19
20// Using \w+ to match words, g flag for all matches
21console.log(str.match(/\w+/g)); // ["The", "rain", "in", "SPAIN", ...]

1let str = "Hello World! HELLO JavaScript!";
2
3// Basic search (case-sensitive)
4console.log(str.search(/World/)); // 6
5
6// Using i flag for case-insensitive search
7console.log(str.search(/hello/i)); // 0
8
9// Note: search() ignores g flag as it only returns first match
10console.log(str.search(/hello/gi)); // 0
11
12// Pattern not found
13console.log(str.search(/Python/)); // -1

1let str = "Test1 test2 TEST3";
2
3// g flag is required for matchAll
4// i flag for case-insensitive matching
5let matches = [...str.matchAll(/test\d/gi)];
6
7// Each match object contains:
8// - The full match
9// - Index where match was found
10// - Input string
11// - Groups (if any)
12console.log(matches);
13// [
14//   ['Test1', index: 0, input: 'Test1 test2 TEST3', groups: undefined],
15//   ['test2', index: 6, input: 'Test1 test2 TEST3', groups: undefined],
16//   ['TEST3', index: 12, input: 'Test1 test2 TEST3', groups: undefined]
17// ]
18
19// Using capture groups with g flag
20let str2 = "2023-03-14 2024-01-01";
21let dateMatches = [...str2.matchAll(/(\d{4})-(\d{2})-(\d{2})/g)];
22dateMatches.forEach(match => {
23  console.log(`Full date: ${match[0]}`);
24  console.log(`Year: ${match[1]}, Month: ${match[2]}, Day: ${match[3]}`);
25});