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To install the TypeScript definitions for Bun’s built-in APIs, install @types/bun. 
bun add -d @types/bun # dev dependency
At this point, you should be able to reference the Bun global in your TypeScript files without seeing errors in your editor. 
console.log(Bun.version);

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Suggested compilerOptions

Bun supports things like top-level await, JSX, and extensioned .ts imports, which TypeScript doesn’t allow by default. Below is a set of recommended compilerOptions for a Bun project, so you can use these features without seeing compiler warnings from TypeScript. 
{  "compilerOptions": {  // Environment setup & latest features  "lib": ["ESNext"],  "target": "ESNext",  "module": "Preserve",  "moduleDetection": "force",  "jsx": "react-jsx",  "allowJs": true,   // Bundler mode  "moduleResolution": "bundler",  "allowImportingTsExtensions": true,  "verbatimModuleSyntax": true,  "noEmit": true,   // Best practices  "strict": true,  "skipLibCheck": true,  "noFallthroughCasesInSwitch": true,  "noUncheckedIndexedAccess": true,  "noImplicitOverride": true,   // Some stricter flags (disabled by default)  "noUnusedLocals": false,  "noUnusedParameters": false,  "noPropertyAccessFromIndexSignature": false,  }, }
If you run bun init in a new directory, this tsconfig.json will be generated for you. (The stricter flags are disabled by default.) 
bun init