Cross-Origin Issues in JavaScript I. Core Issues Browser implements the Same-Origin Policy (SOP) to restrict cross-origin requests, prohibiting requests to servers with different origins (protocol, domain, or port). Primary solutions include: 1. CORS (Cross-Origin Resource Sharing) - Server configures response headers with Access-Control-Allow-Origin to allow specified or all origins - Example (Node.js/Express): ```javascript app.use((req, res) => { res.header('Access-Control-Allow-Origin', '*'); res.header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE'); res.header('Access-Control-Allow-Headers', 'Content-Type'); next(); }) ``` - Preferred solution: Modern browsers' standard implementation, supports multiple HTTP methods and headers 2. JSONP (Only supports GET requests) - Uses