Strings.md

Strings in JavaScript with ES6+

Table of Contents

Introduction to Strings String Declaration - Template Literals String Methods - Common String Methods - ES6+ String Methods String Properties String Concatenation String Comparison

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Introduction to Strings

Strings are a fundamental data type in JavaScript used to represent textual data. With the introduction of ES6, JavaScript added several new features and methods to make string manipulation more powerful and flexible.

String Declaration

Template Literals

Template literals, introduced in ES6, allow embedding expressions inside strings using backticks (`). They support multi-line strings and embedded expressions.

const name = 'John';
const greeting = `Hello, ${name}!
Welcome to our website.`;
console.log(greeting);

Output:

Hello, John! Welcome to our website.

String Methods

Common String Methods

Method	Description	Example
str.length	Returns the length of the string	const len = 'hello'.length; // 5
str.charAt(index)	Returns the character at the specified index	const char = 'hello'.charAt(1); // 'e'
str.indexOf(substring)	Returns the index of the first occurrence of a substring	const index = 'hello'.indexOf('l'); // 2
str.lastIndexOf(substring)	Returns the index of the last occurrence of a substring	const lastIndex = 'hello'.lastIndexOf('l'); // 3
str.slice(start, end)	Extracts a section of a string and returns it as a new string	const sliced = 'hello'.slice(1, 4); // 'ell'
str.substring(start, end)	Returns the part of the string between the start and end indexes	const sub = 'hello'.substring(1, 4); // 'ell'
str.toLowerCase()	Converts a string to lowercase letters	const lower = 'HELLO'.toLowerCase(); // 'hello'
str.toUpperCase()	Converts a string to uppercase letters	const upper = 'hello'.toUpperCase(); // 'HELLO'
str.trim()	Removes whitespace from both ends of a string	const trimmed = ' hello '.trim(); // 'hello'
str.replace(searchValue, replaceValue)	Replaces a specified value with another value in a string	const replaced = 'hello'.replace('l', 'x'); // 'hexlo'

ES6+ String Methods

Method	Description	Example
str.includes(substring)	Determines whether a string contains the specified substring	const includes = 'hello'.includes('ell'); // true
str.startsWith(substring)	Determines whether a string starts with the specified substring	const startsWith = 'hello'.startsWith('he'); // true
str.endsWith(substring)	Determines whether a string ends with the specified substring	const endsWith = 'hello'.endsWith('lo'); // true
str.repeat(count)	Returns a new string with a specified number of copies of the original string	const repeated = 'ha'.repeat(3); // 'hahaha'

String Properties

Property	Description	Example
str.length	Returns the length of the string	const len = 'hello'.length; // 5

String Concatenation

Strings can be concatenated using the + operator or the concat() method.

const str1 = 'Hello';
const str2 = 'World';
const combined = str1 + ' ' + str2; // 'Hello World'
const combined2 = str1.concat(' ', str2); // 'Hello World'

String Comparison

Strings can be compared using comparison operators (<, >, <=, >=, ==, ===).

const str1 = 'apple';
const str2 = 'banana';
console.log(str1 < str2); // true
console.log(str1 === 'apple'); // true

Tip

Use template literals for multi-line strings and embedded expressions. Leverage ES6+ string methods like includes, startsWith, and endsWith for more expressive string operations. Always consider the performance implications of string operations, especially when dealing with large strings.

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