JS String Methods

JavaScript String Methods: Extraction, Transformation, & Searching

JavaScript provides a rich suite of built-in methods for manipulating, extracting, transforming, and padding string data. All string methods return new strings without mutating the original primitive.

Common String Methods Overview

flowchart TD
    Methods["String Methods"] --> Slice["Extraction: slice(), substring(), split()"]
    Methods --> Transform["Transformation: toUpperCase(), toLowerCase(), trim(), replace()"]
    Methods --> Pad["Padding: padStart(), padEnd(), repeat()"]

Key String Transformation Methods

Practical Code Example

// Demonstrating practical string manipulation methods

const rawInput = "   user_name=Maksudur_Rahman; role=admin   ";

// 1. Cleaning and Trimming
const cleanInput = rawInput.trim();
console.log(`Cleaned Input: "${cleanInput}"`);

// 2. Extraction using slice and split
const firstPart = cleanInput.slice(0, 9); // "user_name"
console.log(`Extracted Slice: "${firstPart}"`);

const keyValuePairs = cleanInput.split("; ");
console.log("Split Pairs Array:", keyValuePairs);

// 3. String Replacement
const sanitizedRole = cleanInput.replaceAll("_", " ");
console.log(`Replaced Underscores: "${sanitizedRole}"`);

// 4. Number Padding (Formatting invoice IDs)
const invoiceNumber = 42;
const formattedInvoice = String(invoiceNumber).padStart(6, "0");
console.log(`Formatted Invoice Code: INV-${formattedInvoice}`); // INV-000042

// 5. Case Transformations
console.log(`Upper Case: ${"kodersolution".toUpperCase()}`);

Best Practices & Gotchas

• Prefer slice() Over substring(): slice() accepts negative indices (counting backwards from string end), making it more versatile than substring().
• Use replaceAll() for Global Substitutions: Plain replace("a", "b") replaces only the FIRST match. Use replaceAll() or a global RegExp /a/g.
• Convert Non-Strings Before Padding: Always call String(val) before invoking padStart() or padEnd() on numeric values.

Self-Check Challenge

Format the number 7 as a 3-digit string "007" using padStart().