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String Methods

In JavaScript, strings come with built-in methods that allow you to manipulate and inspect text easily. Understanding these methods helps in tasks like searching, modifying, and formatting strings.

Illustration of string_methods
Illustration of string_methods

💡 What are String Methods?

String methods are functions available on string values to perform operations such as finding substrings, changing case, trimming spaces, and more.

Common String Methods

String Methods Overview
MethodDescriptionExample (" Hello ")
lengthProperty returning the total number of characters in the string." Hello ".length → 7
toUpperCase()Returns a new string with all characters converted to uppercase." Hello ".toUpperCase() → " HELLO "
toLowerCase()Returns a new string with all characters converted to lowercase." Hello ".toLowerCase() → " hello "
trim()Returns a new string with whitespace removed from both ends." Hello ".trim() → "Hello"
indexOf(str)Returns the starting index of a substring (returns -1 if not found)." Hello ".indexOf("e") → 2
includes(str)Returns true if the string contains the substring, otherwise false." Hello ".includes("ll") → true
slice(start, end)Extracts a portion of a string from start index up to end index." Hello ".slice(1, 5) → "Hell"
replace(old, new)Returns a new string with the first occurrence of a substring replaced." Hello ".replace("H", "Y") → " Yello "
split(sep)Splits the string into an array of substrings based on the separator." Hello ".split("e") → [" H", "llo "]

📌 Deep Dive: Using Popular String Methods

JAVASCRIPT
const message = "  Hello, JavaScript!  ";

console.log(message.length);           // 22 (includes spaces)
console.log(message.trim());           // "Hello, JavaScript!"
console.log(message.toUpperCase());    // "  HELLO, JAVASCRIPT!  "
console.log(message.toLowerCase());    // "  hello, javascript!  "
console.log(message.indexOf("Java"));  // 8
console.log(message.includes("script")); // true
console.log(message.slice(2, 7));      // "Hello"
console.log(message.replace("JavaScript", "JS")); // "  Hello, JS!  "
console.log(message.trim().split(", ")); // ["Hello", "JavaScript!"]
Output
22
"Hello, JavaScript!"
" HELLO, JAVASCRIPT! "
" hello, javascript! "
8
true
"Hello"
" Hello, JS! "
["Hello", "JavaScript!"]

💡 Remember:

Strings in JavaScript are immutable. Methods like toUpperCase() and replace() return new strings—they do not change the original.

⚠️ Common Pitfall

Using indexOf() to check if a substring exists requires checking for >= 0, because it returns -1 if not found. For clarity, prefer includes() which returns a boolean.

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