🏷️ Strings

In JavaScript, a String is a text type represented using UTF-16 encoding. Strings can be created using:

• Double quotes ("")
• Single quotes ('')
• Backticks (``) → (Template Literal)

1. Ways to Create Strings

Example: Strings created in different ways

    const str1 = "Hello"; // Double quotes
    const str2 = 'World'; // Single quotes
    const str3 = `Welcome, ${str1} ${str2}!`; // Backticks (Template Literal)

Template Literal allows embedding variables using ${}:

    const name = "John";
    const message = `Hello, ${name}!`; // Hello, John!

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2. Key Properties of Strings

Indexing

• Strings can be treated as array-like structures.
• Indexing starts at 0.

    const str = 'JavaScript';
    console.log(str[0]); // 'J'
    console.log(str[4]); // 'S'
    console.log(str[str.length - 1]); // 't'

Immutability

• Strings are immutable—they cannot be modified directly.
• To "change" a string, you must create a new one.

    let str = 'Hello';
    str[0] = 'h'; // Won't work
    str = 'hello'; // Reassignment works

3. Essential Methods

JavaScript provides several built-in string methods:

length → Returns string length

    const str = 'JavaScript';
    console.log(str.length); // 10

charAt(index) → Returns character at the specified index

    const str = 'JavaScript';
    console.log(str.charAt(0)); // 'J'

slice(start, end) → Extracts a substring

• start → Starting index
• end → (Optional) End index (exclusive)

    const str = 'JavaScript';
    console.log(str.slice(0, 4)); // 'Java'
    console.log(str.slice(4));   // 'Script'
    console.log(str.slice(-6));  // 'Script'

substring(start, end) → Similar to slice but ignores negative values

    const str = 'JavaScript';
    console.log(str.substring(0, 4)); // 'Java'
    console.log(str.substring(4));   // 'Script'

substr(start, length) → Extracts a substring with a specified length

    const str = 'JavaScript';
    console.log(str.substr(4, 3)); // 'Scr'

toUpperCase() & toLowerCase() → Changes text case

    const str = 'JavaScript';
    console.log(str.toUpperCase()); // 'JAVASCRIPT'
    console.log(str.toLowerCase()); // 'javascript'

trim() → Removes whitespace from both ends

    const str = '   Hello World!   ';
    console.log(str.trim()); // 'Hello World!'

replace() → Replaces a character or substring

    const str = 'JavaScript is great';
    console.log(str.replace('great', 'awesome')); // 'JavaScript is awesome'

replace() changes only the first match.

Use a regular expression (RegEx) to replace all occurrences:

    const str = 'JavaScript is great, JavaScript is fun';
    console.log(str.replace(/JavaScript/g, 'JS')); // 'JS is great, JS is fun'

split() → Splits a string into an array using a delimiter

    const str = 'JavaScript is fun';
    console.log(str.split(' ')); // ['JavaScript', 'is', 'fun']

includes() → Returns true if the substring exists

    const str = 'JavaScript is fun';
    console.log(str.includes('Script')); // true
    console.log(str.includes('script')); // false (case-sensitive)

startsWith() & endsWith()

    const str = 'JavaScript';
    console.log(str.startsWith('Java')); // true
    console.log(str.endsWith('Script')); // true

String Concatenation

Using the + operator

    const firstName = 'John';
    const lastName = 'Doe';
    const fullName = firstName + ' ' + lastName;
    console.log(fullName); // 'John Doe'

Using concat()

    const firstName = 'John';
    const lastName = 'Doe';
    const fullName = firstName.concat(' ', lastName);
    console.log(fullName); // 'John Doe'

Using Template Literal

    const firstName = 'John';
    const lastName = 'Doe';
    const fullName = `${firstName} ${lastName}`;
    console.log(fullName); // 'John Doe'

String vs String Object

Strings can also be created as objects using new String(), but this is not recommended.

    const str1 = 'Hello'; // String type
    const str2 = new String('Hello'); // String object
        
    console.log(typeof str1); // 'string'
    console.log(typeof str2); // 'object'
    console.log(str1 === str2); // false

Best practice: Use primitive strings instead of String objects.

Best Practices

• Prefer Template Literals (\``) for clarity and readability.
• Avoid String objects.
• Use includes() and startsWith() for checks.
• Use replaceAll() or RegEx for global replacements.