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# Strip Final Newline
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Strip Final Newline is a lightweight utility that removes the final newline character from strings and Uint8Array objects. It handles both string inputs and binary data, correctly identifying and removing trailing newline characters (`\n`) and carriage return + newline combinations (`\r\n`). The library is particularly useful for processing output from child processes and command-line tools that typically append trailing newlines.
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## Package Information
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- **Package Name**: strip-final-newline
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- **Package Type**: npm
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- **Language**: JavaScript (ES Module)
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- **Installation**: `npm install strip-final-newline`
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## Core Imports
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```javascript
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import stripFinalNewline from "strip-final-newline";
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```
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Note: This package is ES module only (`"type": "module"` in package.json) and does not support CommonJS `require()`.
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## Basic Usage
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```javascript
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import stripFinalNewline from "strip-final-newline";
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// String input
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stripFinalNewline('foo\nbar\n\n');
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//=> 'foo\nbar\n'
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stripFinalNewline('hello world\n');
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//=> 'hello world'
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stripFinalNewline('no newline');
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//=> 'no newline'
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// Uint8Array input  
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const uint8Array = new TextEncoder().encode('foo\nbar\n\n');
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const result = stripFinalNewline(uint8Array);
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new TextDecoder().decode(result);
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//=> 'foo\nbar\n'
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// Handles both LF and CRLF
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stripFinalNewline('windows line ending\r\n');
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//=> 'windows line ending'
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```
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## Capabilities
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### Strip Final Newline Function
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Removes the final newline character from a string or Uint8Array input. For strings, it removes the final `\n` or `\r\n` sequence. For Uint8Array inputs, it uses efficient subarray operations that reference the original data rather than copying it.
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```typescript { .api }
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/**
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 * Strip the final newline character from a string or Uint8Array
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 * @param input - The input to strip final newline from
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 * @returns The input without any final newline, preserving the original type
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 * @throws Error if input is not a string or Uint8Array
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 */
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function stripFinalNewline<T extends string | Uint8Array>(input: T): T;
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```
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**Parameters:**
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- `input`: string | Uint8Array - The input data to process
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**Returns:**
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- Same type as input (string or Uint8Array) with final newline removed
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**Behavior:**
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- For strings: Removes final `\n` character or `\r\n` sequence
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- For Uint8Array: Returns subarray reference (no copying) with final newline bytes removed
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- Preserves all internal newlines and whitespace - only removes the final newline
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- If input has no final newline, returns the input unchanged
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- Throws `Error` with message "Input must be a string or a Uint8Array" for invalid input types
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**Performance Notes:**
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- String processing creates a new string with final characters removed
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- Uint8Array processing returns a subarray reference for maximum efficiency
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- No memory copying for Uint8Array inputs - operates in constant time regardless of input size
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- For guaranteed immutability with Uint8Array results, use `.slice()` on the returned value
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**Usage Examples:**
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```javascript
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import stripFinalNewline from "strip-final-newline";
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// Basic string processing
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const output = stripFinalNewline('command output\n');
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console.log(`"${output}"`); // "command output"
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// Processing child process output
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import { execSync } from 'child_process';
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const rawOutput = execSync('echo "hello world"', { encoding: 'utf8' });
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const cleanOutput = stripFinalNewline(rawOutput);
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// Binary data processing (efficient - no copying)
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const binaryData = new TextEncoder().encode('data\n');
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const stripped = stripFinalNewline(binaryData);
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// stripped is a subarray reference to binaryData
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// Ensuring immutability for binary data
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const immutableResult = stripFinalNewline(binaryData).slice();
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```
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## Error Handling
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The function validates input types and throws descriptive errors:
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```javascript
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// These will throw Error: "Input must be a string or a Uint8Array"
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stripFinalNewline(123);           // number
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stripFinalNewline(true);          // boolean  
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stripFinalNewline(['a', 'b']);    // array
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stripFinalNewline(new DataView(new ArrayBuffer(0))); // DataView
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stripFinalNewline(new Uint16Array(0)); // Uint16Array (wrong element size)
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```
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## Types
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```typescript { .api }
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// Generic function signature with type preservation
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function stripFinalNewline<T extends string | Uint8Array>(input: T): T;
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// Union type for all valid inputs
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type ValidInput = string | Uint8Array;
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```