Bun is a fast-growing JavaScript runtime with its own vocabulary and APIs. Whether adopting it or evaluating it, you'll need to discuss its trade-offs confidently in English.
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A developer says: 'Let's try Bun for the scripts — it's much faster than Node.' What is Bun?
Bun is an all-in-one JavaScript runtime built on JavaScriptCore (the Safari engine) rather than V8. It bundles a runtime, bundler, package manager (bun install), and test runner. It's known for significantly faster startup times and install speeds compared to Node.js. In conversations: 'use Bun for scripts' means leverage its speed for build steps or CLI tools where startup overhead matters.
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A developer says: 'Bun uses Bun.file() instead of Node's fs module.' What does this comparison tell you?
Bun provides Bun-native APIs (like Bun.file(), Bun.serve()) that are optimised for its runtime. While Bun aims for Node.js compatibility, it also offers its own abstractions. In discussions: 'use Bun.file()' signals the dev is intentionally using Bun's optimised API rather than the Node.js-compatible fs module. This trade-off (performance vs portability) is a common architecture point.
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In a team discussion: 'We should use Bun's built-in bundler instead of Vite for this CLI tool.' What is a bundler?
A bundler takes your source files (multiple modules, imports) and combines them into one or a few output files. It resolves imports, applies transformations (TypeScript, JSX), and optionally minifies. Bun has a built-in bundler (bun build) that is fast for CLI tools and libraries. The comparison 'use Bun bundler instead of Vite' contrasts two different bundling tools and their trade-offs.
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A developer mentions: 'Bun supports hot module reloading with --hot.' What does hot reloading mean?
Hot Module Reloading (HMR) means changed modules are swapped into the running process without a full restart. For development servers, this means seeing changes reflected instantly while preserving state (no page refresh). Bun's --hot flag enables this for Bun processes. In developer experience discussions: 'does it support HMR?' is about how fast the developer feedback loop is during development.
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A developer says: 'Bun is drop-in compatible with Node.js for most use cases.' What does drop-in compatible mean?
Drop-in compatible means you can substitute one tool for another without rewriting your code. Bun implements Node.js APIs (fs, path, http, etc.) so most Node.js code runs under Bun unchanged. In migration discussions: 'it's drop-in compatible' means the risk of switching is low — you change the runtime command (bun run instead of node) but keep the same codebase.