Simple Markdown to HTML Parser

This challenge asks you to build a basic Markdown parser in JavaScript. Markdown is a lightweight markup language that allows you to format plain text using a simple syntax. Converting Markdown to HTML is a common task in web development, enabling rich text editing and display.

Problem Description

Your task is to create a JavaScript function, parseMarkdown, that takes a string containing Markdown syntax as input and returns a string representing the equivalent HTML. This parser should handle a limited set of Markdown features:

• Headings: Markdown uses # for headings.
  • # Heading 1 should become <h1>Heading 1</h1>
  • ## Heading 2 should become <h2>Heading 2</h2>
  • And so on, up to ###### Heading 6.
• Bold Text: Markdown uses ** to denote bold text.
  • This is **bold** text. should become This is <strong>bold</strong> text.
• Italic Text: Markdown uses * to denote italic text.
  • This is *italic* text. should become This is <em>italic</em> text.
• Paragraphs: Plain text lines that are not recognized as other Markdown elements should be wrapped in <p> tags. Blank lines should separate paragraphs.

Key Requirements:

• The function should accept a single string argument representing the Markdown input.
• The function should return a single string representing the generated HTML output.
• The parser should process the Markdown line by line.
• The order of operations matters: you should handle bold and italic text within lines before wrapping lines in paragraph tags.

Expected Behavior:

The parser should accurately translate the specified Markdown elements into their corresponding HTML tags.

Edge Cases to Consider:

• Empty input string.
• Input with only whitespace.
• Lines that start with Markdown syntax but don't conform perfectly (e.g., # followed by a space).
• Nested bold/italic (though for this basic parser, assume no deep nesting, but handle cases like ***bold and italic***).
• Markdown syntax appearing within code blocks (this is a more advanced case, but for this basic challenge, you can assume no code blocks).

Examples

Example 1:

Input:
# This is a Heading

This is a **bold** paragraph.
This is an *italic* paragraph.

Output:
<h1>This is a Heading</h1>
<p>This is a <strong>bold</strong> paragraph.</p>
<p>This is an <em>italic</em> paragraph.</p>

Explanation: The first line is a level 1 heading. The subsequent lines are treated as paragraphs, with bold and italic syntax correctly translated.

Example 2:

Input:
## Another Heading
Some text here.
More text with **bold** and *italic*.
A final line.

A new paragraph.

Output:
<h2>Another Heading</h2>
<p>Some text here.</p>
<p>More text with <strong>bold</strong> and <em>italic</em>.</p>
<p>A final line.</p>
<p>A new paragraph.</p>

Explanation: Handles multiple paragraphs and different heading levels. Notice how the blank line correctly separates the last paragraph of the first block from the new paragraph.

Example 3:

Input:
***Bold and Italic***
# Heading with ***bold***

Output:
<p><em><strong>Bold and Italic</strong></em></p>
<h1>Heading with <strong>bold</strong></h1>

Explanation: Demonstrates that *** should be interpreted as both bold and italic (order of application might matter here, leading to <em><strong>...</strong></em> or <strong><em>...</em></strong> – <em><strong> is a reasonable outcome for this basic implementation). Also shows heading processing taking precedence over general paragraph formatting.

Constraints

• The input Markdown string will not exceed 10,000 characters.
• The input will be a valid JavaScript string.
• The output should be a valid HTML string.
• Performance is not a critical constraint for this challenge, but the solution should be reasonably efficient.
• Focus on correctly implementing the specified Markdown features. Do not implement other Markdown features like lists, links, images, or code blocks.

Notes

• Consider using regular expressions to identify and replace Markdown syntax.
• Think about how to process the input string efficiently, perhaps by splitting it into lines.
• The order of operations is important. For example, you should apply bold and italic transformations before wrapping lines in paragraph tags.
• For the *** case, consider which tag should be on the outside. A common interpretation is to apply both, resulting in nested tags or combined <strong><em>.