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The most widely used programming language for web development, running in browsers and on servers via Node.js.
Created by Brendan Eich at Netscape in 1995 and standardized as ECMAScript, JavaScript has grown from a simple browser scripting language into the most widely deployed programming language in the world. It runs natively in every web browser, powers server-side applications through Node.js and Deno, and extends into mobile development with React Native, desktop apps with Electron, and even IoT devices. The language supports multiple paradigms — event-driven, functional, and object-oriented — with prototypal inheritance rather than classical class hierarchies. Modern JavaScript (ES2015+) introduced modules, arrow functions, async/await, destructuring, and iterators, fundamentally reshaping how developers structure applications.
The ecosystem is enormous: npm hosts over two million packages, and frameworks like React, Vue, Angular, and Svelte dominate front-end development. Build tools such as Vite, webpack, and esbuild handle bundling, transpilation, and optimization. On the server side, Express, Fastify, and Hono power APIs ranging from startups to Fortune 500 companies. TypeScript, a typed superset, further expanded JavaScript's reach into large-scale enterprise codebases.
The language evolves through the TC39 proposal process, with annual specification releases adding features like top-level await, structuredClone, and the Temporal API. Despite criticism of its quirks — loose typing, coercion rules, and the event loop's single-threaded model — JavaScript's ubiquity and low barrier to entry make it the default language for building anything that touches the web.
JavaScript changes can silently alter runtime behavior due to loose typing, coercion, and hoisting. Comparing files catches accidental scope changes from var to let/const swaps, broken destructuring patterns, modified async flow that introduces race conditions, and dependency import reordering that affects tree-shaking.
Front-end teams diff component logic, event handlers, and API calls during code review. Build configuration changes in bundler configs also demand careful comparison to avoid production regressions.
UtraDiff opens JavaScript files in a diff editor with full ES/JSX syntax highlighting, showing additions, deletions, and modifications in side-by-side or inline views. Language-aware tokenization distinguishes keyword changes from identifier renames.
Toggle whitespace ignore so ES module import reordering and auto-formatter spacing won't trigger false positives. Navigate between changes with Alt+Arrow keys, and use the case-insensitive toggle to focus on logic rather than naming conventions.
Supported extensions: .js .jsx .mjs .cjs