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# Configuration and Authentication
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Configuration settings for the Tinify client including API key authentication, proxy settings, and application identification.
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## Capabilities
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### API Key Authentication
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Set your Tinify API key for authentication. This is required before using any image processing functionality.
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```typescript { .api }
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/**
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 * Set the API key for authentication with the Tinify API
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 * @example tinify.key = "your-api-key-here"
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 */
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let key: string;
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```
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**Usage Example:**
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```typescript
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const tinify = require("tinify");
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// Set API key (required)
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tinify.key = "your-api-key-here";
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// Now you can use image processing methods
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await tinify.fromFile("image.png").toFile("compressed.png");
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```
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### Application Identifier
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Set an application identifier to be included in the user agent string for API requests.
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```typescript { .api }
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/**
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 * Set application identifier for user agent string
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 * @example tinify.appIdentifier = "MyApp/1.0"
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 */
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let appIdentifier: string;
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```
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**Usage Example:**
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```typescript
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const tinify = require("tinify");
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tinify.key = "your-api-key";
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tinify.appIdentifier = "MyApp/1.0";
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// User agent will include: "Tinify/1.8.1 Node/v14.15.0 (linux) MyApp/1.0"
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```
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### Proxy Configuration
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Configure proxy settings for API requests when operating behind a corporate proxy.
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```typescript { .api }
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/**
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 * Set proxy URL for API requests
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 * @example tinify.proxy = "http://proxy.example.com:8080"
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 */
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let proxy: string;
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```
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**Usage Example:**
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```typescript
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const tinify = require("tinify");
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tinify.key = "your-api-key";
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tinify.proxy = "http://proxy.example.com:8080";
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```
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### Compression Count
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Read-only property that tracks the number of compressions made with your API key this month.
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```typescript { .api }
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/**
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 * Current compression count from API headers (read-only)
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 * Updated automatically after each API request
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 */
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let compressionCount?: number;
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```
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**Usage Example:**
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```typescript
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const tinify = require("tinify");
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tinify.key = "your-api-key";
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await tinify.fromFile("image.png").toFile("compressed.png");
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console.log(`Compressions used: ${tinify.compressionCount}`);
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```
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### API Key Validation
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Validate your API key without performing actual image compression.
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```typescript { .api }
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/**
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 * Validate API key without performing compression
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 * @returns Promise that resolves if key is valid, rejects on error
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 */
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function validate(): Promise<void>;
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/**
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 * Validate API key with callback support
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 * @param callback - Callback function receiving error or null
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 */
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function validate(callback: (err: Error | null) => void): void;
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```
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**Usage Examples:**
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```typescript
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const tinify = require("tinify");
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tinify.key = "your-api-key";
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// Promise-based validation
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try {
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  await tinify.validate();
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  console.log("API key is valid");
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} catch (error) {
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  console.error("Invalid API key:", error.message);
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}
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// Callback-based validation
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tinify.validate((err) => {
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  if (err) {
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    console.error("Invalid API key:", err.message);
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  } else {
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    console.log("API key is valid");
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  }
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});
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```
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## Error Handling
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Configuration methods can throw the following errors:
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- **AccountError**: Invalid API key, exceeded monthly limit, or billing issues
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- **ConnectionError**: Network connectivity problems
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- **ClientError**: Invalid proxy URL or malformed requests