Dead Code Eliminator in JavaScript

Dead code, also known as unreachable code, is code that can never be executed during the normal operation of a program. Identifying and removing dead code improves code readability, reduces bundle size, and can potentially reveal underlying logic errors. This challenge asks you to create a JavaScript function that analyzes a given JavaScript code string and identifies and removes dead code.

Problem Description

You are tasked with creating a JavaScript function called eliminateDeadCode that takes a string containing JavaScript code as input and returns a new string with all dead code removed. Dead code is defined as code that is unreachable due to control flow statements like return, throw, break, continue, or exit. The function should analyze the code and remove any blocks of code that are guaranteed to never be executed.

Key Requirements:

• Input: A string containing valid JavaScript code.
• Output: A string containing the original JavaScript code with all dead code removed.
• Analysis: The function must accurately identify unreachable code blocks.
• Preservation: The function must preserve the functionality of the original code; removing dead code should not alter the behavior of the program when executed with valid inputs.
• No External Libraries: You are not allowed to use external JavaScript libraries for parsing or analysis. You must implement the logic yourself.

Expected Behavior:

The function should handle various scenarios, including:

• Code blocks after return, throw, break, continue, and exit statements.
• Nested control flow statements.
• Functions with multiple return statements.
• Empty code blocks.
• Comments (should be preserved unless they are part of dead code).

Edge Cases to Consider:

• Empty input string.
• Code with no dead code.
• Code with complex nested control flow.
• Code with comments within dead code blocks.
• Code with try...catch blocks where the catch block is unreachable.

Examples

Example 1:

Input: `function foo() { return 1; console.log('This will not be printed'); }`
Output: `function foo() { return 1; }`
Explanation: The `console.log` statement is unreachable because it follows a `return` statement.

Example 2:

Input: `function bar(x) { if (x > 5) { throw new Error("x is too large"); } console.log("x is not too large"); return x; }`
Output: `function bar(x) { if (x > 5) { throw new Error("x is too large"); } return x; }`
Explanation: The `console.log` statement is unreachable because it follows a `throw` statement.

Example 3:

Input: `function baz() { console.log("First"); break; console.log("Second"); }`
Output: `function baz() { console.log("First"); break; }`
Explanation: The `console.log("Second")` statement is unreachable because it follows a `break` statement.

Example 4:

Input: `function qux() { console.log("Start"); continue; console.log("Middle"); console.log("End"); }`
Output: `function qux() { console.log("Start"); continue; }`
Explanation: The `console.log("Middle")` and `console.log("End")` statements are unreachable because they follow a `continue` statement.

Constraints

• Input String Length: The input JavaScript code string can be up to 10,000 characters.
• Input Format: The input must be a string containing valid JavaScript code. While perfect validation isn't required, the code should be reasonably well-formed.
• Performance: The function should complete within 1 second for the given input length. While a perfect solution is prioritized, efficiency is a consideration.
• No External Libraries: As mentioned, no external libraries are allowed.

Notes

This is a challenging problem that requires careful consideration of JavaScript's control flow. A simple approach might involve parsing the code into an Abstract Syntax Tree (AST), but you are not allowed to use external libraries for this. You'll need to implement a strategy for analyzing the code string directly, potentially using regular expressions or string manipulation techniques. Consider how to track the execution path and identify unreachable blocks. Remember to handle comments appropriately – they should generally be preserved unless they are part of dead code. Focus on correctness first, then optimize for performance if needed.