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# Environment Variables
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Cross-platform environment variable access that works consistently across Node.js, Deno, Bun, and browser environments using a Proxy-based approach.
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## Capabilities
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### Environment Variable Proxy
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The `env` proxy provides universal access to environment variables across different JavaScript runtimes.
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```typescript { .api }
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/**
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 * Cross-platform environment variable proxy that works across all JavaScript runtimes
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 * Supports Node.js process.env, Deno.env, import.meta.env, and browser globalThis.__env__
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 */
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const env: EnvObject;
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type EnvObject = Record<string, string | undefined>;
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```
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**Usage Examples:**
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```typescript
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import { env } from "std-env";
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// Read environment variables
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const apiKey = env.API_KEY;
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const nodeEnv = env.NODE_ENV;
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const port = env.PORT || "3000";
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// Set environment variables (when possible)
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env.DEBUG = "true";
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// Check if environment variable exists
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if ("DATABASE_URL" in env) {
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  console.log("Database URL is configured");
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}
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// Iterate over environment variables
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for (const key of Object.getOwnPropertyNames(env)) {
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  console.log(`${key}: ${env[key]}`);
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}
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```
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The `env` proxy automatically detects the runtime and uses the appropriate environment access method:
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- **Node.js**: `process.env`
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- **Deno**: `Deno.env.toObject()`
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- **Vite/Rollup**: `import.meta.env`
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- **Browser/Custom**: `globalThis.__env__`
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### Node.js Environment Variable
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Direct access to the NODE_ENV environment variable with fallback to empty string.
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```typescript { .api }
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/**
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 * Value of NODE_ENV environment variable or empty string if not set
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 * Specifically reads from process.env.NODE_ENV when available
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 */
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const nodeENV: string;
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```
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**Usage Examples:**
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```typescript
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import { nodeENV } from "std-env";
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// Check specific Node.js environment
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if (nodeENV === "production") {
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  console.log("Running in production mode");
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} else if (nodeENV === "development") {
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  console.log("Running in development mode");
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} else if (nodeENV === "test") {
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  console.log("Running in test mode");
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}
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// Use as fallback when env proxy might not be available
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const environment = nodeENV || "development";
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```
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## Runtime Compatibility
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The environment variable system works across all supported JavaScript runtimes:
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- **Node.js**: Uses `process.env` directly
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- **Deno**: Uses `Deno.env.toObject()` for read access
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- **Bun**: Compatible with Node.js `process.env`
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- **Browser**: Uses `import.meta.env` (Vite/bundlers) or `globalThis.__env__`
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- **Edge Runtimes**: Falls back to available global environment objects