JavaScript String Methods

In this tutorial, you will learn about various string methods in JavaScript.

String Length

The length property provides the number of characters contained in a string.

let x = "WebmasterMaze";

console.log(x.length); // Output: 13

Extracting String Characters

JavaScript provides several methods to extract characters from a string:

Using charAt()

The charAt() method retrieves the character located at a specified index (position) within a string.

var x = "WebmasterMaze";

console.log(x.charAt(4)); // Output: a

Using charCodeAt()

The charCodeAt() method in JavaScript returns the Unicode (UTF-16) code of the character at a specified index in a string. The returned value is an integer between 0 and 65535.

let x = "WebmasterMaze";

console.log(x.charCodeAt(0)); // Output: 119

Using at()

Similar to charAt(), but supports negative indexing.

const name = "WebmasterMaze";
let letter = name.at(2);

console.log(letter); // Output: b

Using Bracket [] Notation

Simplest way to access a character. Does not support negative indexing.

const name = "WebmasterMaze";
let letter = name[2];

console.log(letter); // Output: b

Extracting String Parts

JavaScript provides three methods for extracting parts of a string:

slice(start, end)

• Extracts a portion of a string and returns it as a new string.
• Supports negative indexes (counts from the end).
• The end index is exclusive (not included).

let text = "JavaScript Programming";
console.log(text.slice(0, 10));   // Output: "JavaScript"
console.log(text.slice(11));      // Output: "Programming" (Extracts from index 11 to the end)
console.log(text.slice(-11));     // Output: "Programming" (Negative index starts from the end)
console.log(text.slice(-11, -6)); // Output: "Progr"

substring(start, end)

• Similar to slice(), but does not support negative indexes.
• If start > end, it swaps them automatically.

console.log(text.substring(0, 10));  // Output: "JavaScript"
console.log(text.substring(11));     // Output: "Programming"
console.log(text.substring(10, 0));  // Output: "JavaScript" (Swaps automatically)
console.log(text.substring(-5, 10)); // Output: "JavaScript" (Negative index is treated as 0)

substr(start, length)

• Extracts a portion of a string based on length.
• Supports negative indexes for start.
• length defines how many characters to extract.

console.log(text.substr(0, 10));   // Output: "JavaScript"
console.log(text.substr(11, 5));   // Output: "Progr"
console.log(text.substr(-11, 5));  // Output: "Progr" (Starts from the 11th character from the end)

Converting Strings to Uppercase and Lowercase

JavaScript provides built-in methods to convert a string to uppercase or lowercase easily:

toUpperCase()

This method returns a new string with all letters in uppercase.

let text = "Hello World";
console.log(text.toUpperCase()); // Output: "HELLO WORLD"

• Works on both letters and mixed-case strings.
• Does not modify the original string (strings are immutable).

toLowerCase()

This method returns a new string with all letters in lowercase.

console.log(text.toLowerCase()); // Output: "hello world"

• Useful for case-insensitive comparisons.

String concat() Method

The concat() method in JavaScript is used to join two or more strings and return a new combined string.

let firstName = "John";
let lastName = "Doe";

let fullName = firstName.concat(" ", lastName);
console.log(fullName); // Output: "John Doe"

• It does not modify the original strings.
• You can concatenate multiple strings at once.
• Spaces must be added manually if needed.
• Use + or template literals (${}) for simple concatenation.
• Use join() if you’re dealing with arrays.
• Avoid concat() unless necessary.

String trim()

The trim() method eliminates any leading and trailing whitespace from a string.

let text = "   WebmasterMaze!   ";

console.log(text.trim());      // Output: "WebmasterMaze!"  (Removes spaces from both ends)
console.log(text.trimStart()); // Output: "WebmasterMaze!   " (Removes spaces from the start)
console.log(text.trimEnd());   // Output: "   WebmasterMaze!" (Removes spaces from the end)

String Padding Method

JavaScript provides two methods for padding a string:

• padStart(targetLength, padString)
• padEnd(targetLength, padString) 

let text = "42";

console.log(text.padStart(5, "0")); // Output: "00042"  (Pads with "0" at the start)
console.log(text.padEnd(6, "*"));   // Output: "42****" (Pads with "*" at the end)

console.log("123".padStart(6, "AB")); // Output: "AB123" (Trims excess padding)
console.log("Hello".padEnd(10));      // Output: "Hello     " (Pads with spaces by default)

String repeat() Method

The repeat() method creates a new string by repeating the original string a specified number of times.

Syntax

string.repeat(count)

• count: The number of times to repeat the string (must be ≥ 0).
• Returns a new string, does not modify the original.
• Throws an error if count is negative or Infinity.

let text = "Hello ";
console.log(text.repeat(3));   // Output: "Hello Hello Hello " (Repeats 3 times)
console.log("Hi".repeat(5));   // Output: "HiHiHiHiHi" (No spaces added automatically)
console.log("-".repeat(10));   // Output: "----------" (Useful for separators)
console.log("Test".repeat(0)); // Output: "" (Empty string if count is 0)
// Invalid cases
// console.log("Error".repeat(-1)); // Throws an error

Replacing String Content 

JavaScript provides several ways to replace content within a string.

replace()

Replaces only the first occurrence of a specified value.

let text = "I love JavaScript. JavaScript is fun!";
console.log(text.replace("JavaScript", "PHP")); 
// Output: "I love PHP. JavaScript is fun!"

• Case-sensitive (use /pattern/i for case-insensitive replacement).
• Can use regular expressions for more control.

replaceAll()

Replaces all occurrences of a specified value.

console.log(text.replaceAll("JavaScript", "PHP")); 
// Output: "I love PHP. PHP is fun!"

• Works with strings and regular expressions (/pattern/g).

Using Regular Expressions (/pattern/g)

For replacing all occurrences dynamically:

console.log(text.replace(/JavaScript/g, "PHP")); 
// Output: "I love PHP. PHP is fun!"

• /g (global) ensures all matches are replaced.
• /i (case-insensitive) ignores letter case.

JavaScript split() Method

The split() method divides a string into an array based on a specified separator.

let text = "apple,banana,grape,orange";
// Split by comma
console.log(text.split(",")); 
// Output: ["apple", "banana", "grape", "orange"]

// Split by a character (e.g., "a")
console.log(text.split("a"));  
// Output: ["", "pple,b", "n", "n", "gr", "pe,or", "nge"]

// Split into individual characters
console.log(text.split(""));  
// Output: ["a", "p", "p", "l", "e", ",", "b", "a", "n", "a", "n", "a", ",", "g", "r", "a", "p", "e", ",", "o", "r", "a", "n", "g", "e"]

// Split with a limit (only first 2 elements)
console.log(text.split(",", 2));  
// Output: ["apple", "banana"]

// Split by a space (useful for sentences)
let sentence = "Hello World! JavaScript is awesome.";
console.log(sentence.split(" "));  
// Output: ["Hello", "World!", "JavaScript", "is", "awesome."]

// Split with no separator (returns entire string in an array)
console.log(text.split());  
// Output: ["apple,banana,grape,orange"]