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TYPESCRIPT FUNDAMENTALS - CHALLENGE 2 SOLUTION
Chapter 8: Functions & Overloads
Challenge: Overload with Different Behavior
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PROBLEM:
Create a convertToJSON function that takes an object and optional formatting.
If formatting is true, return pretty JSON. If false, return compact JSON.

SOLUTION:
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// Overload signatures - different behavior based on parameter
function convertToJSON(obj: any, format: true): string;
function convertToJSON(obj: any, format?: false): string;
function convertToJSON(obj: any): string;

// Implementation
function convertToJSON(obj: any, format: boolean = false): string {
  if (format === true) {
    // Pretty print with 2-space indentation
    return JSON.stringify(obj, null, 2);
  } else {
    // Compact JSON with no extra whitespace
    return JSON.stringify(obj);
  }
}

// Testing the solution
const user = {
  id: 1,
  name: "Alice",
  email: "alice@example.com",
  active: true
};

// Pretty JSON (format = true)
console.log("=== Pretty JSON ===");
console.log(convertToJSON(user, true));

// Compact JSON (format = false or omitted)
console.log("\n=== Compact JSON ===");
console.log(convertToJSON(user, false));
console.log(convertToJSON(user));

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EXPECTED OUTPUT:
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=== Pretty JSON ===
{
  "id": 1,
  "name": "Alice",
  "email": "alice@example.com",
  "active": true
}

=== Compact JSON ===
{"id":1,"name":"Alice","email":"alice@example.com","active":true}
{"id":1,"name":"Alice","email":"alice@example.com","active":true}

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WHY THIS WORKS:
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1. Multiple Overload Signatures
   - function convertToJSON(obj: any, format: true): string;
     → For when format is explicitly true
   - function convertToJSON(obj: any, format?: false): string;
     → For when format is false or omitted (default false)
   - function convertToJSON(obj: any): string;
     → For when no format parameter is provided

2. JSON.stringify Parameters
   - JSON.stringify(obj) → compact JSON
   - JSON.stringify(obj, null, 2) → pretty JSON with 2-space indent
   - The third parameter is the indentation level

3. Flexible Default Behavior
   - If format parameter is not provided, defaults to false (compact)
   - This is common for APIs - compact is usually the default

4. Self-Documenting Code
   - The overloads make it clear what the function can do
   - Callers know they can pass true for pretty printing

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ALTERNATIVE APPROACHES:
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Approach 1: Using a literal type union
function convertToJSON(obj: any, format: "pretty" | "compact" = "compact"): string {
  if (format === "pretty") {
    return JSON.stringify(obj, null, 2);
  } else {
    return JSON.stringify(obj);
  }
}

// Callers use descriptive string constants
convertToJSON(user, "pretty");
convertToJSON(user, "compact");

// More readable but longer signatures

Approach 2: Using an options object
interface JSONOptions {
  pretty?: boolean;
  indent?: number;
}

function convertToJSON(obj: any, options: JSONOptions = {}): string {
  const indent = options.pretty ? (options.indent ?? 2) : undefined;
  return JSON.stringify(obj, null, indent);
}

// More flexible for adding more options later
convertToJSON(user, { pretty: true, indent: 4 });

Approach 3: Separate functions (no overloads needed)
function toCompactJSON(obj: any): string {
  return JSON.stringify(obj);
}

function toPrettyJSON(obj: any, indent: number = 2): string {
  return JSON.stringify(obj, null, indent);
}

// Most explicit but requires multiple function names

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ADVANCED VARIATION: WITH CUSTOM INDENT:
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// More powerful version with custom indentation
function convertToJSON(obj: any): string;
function convertToJSON(obj: any, indent: number): string;
function convertToJSON(obj: any, indent?: number): string {
  if (indent === undefined) {
    // No indent = compact
    return JSON.stringify(obj);
  } else if (indent === 0) {
    // Indent 0 = compact (edge case)
    return JSON.stringify(obj);
  } else {
    // Positive indent = pretty print with that indentation
    return JSON.stringify(obj, null, indent);
  }
}

// Usage
console.log(convertToJSON(user));        // Compact
console.log(convertToJSON(user, 2));     // Pretty with 2 spaces
console.log(convertToJSON(user, 4));     // Pretty with 4 spaces
console.log(convertToJSON(user, 0));     // Compact

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REAL-WORLD EXAMPLES:
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Example 1: Logging with Different Levels
function log(message: any): void;
function log(message: any, verbose: true): void;
function log(message: any, verbose: boolean = false): void {
  if (verbose) {
    console.log("[VERBOSE]", JSON.stringify(message, null, 2));
  } else {
    console.log("[INFO]", message);
  }
}

log("User logged in");
log({ user: "alice", timestamp: Date.now() }, true);

Example 2: API Response Formatter
function formatResponse(data: any, minify: boolean = false): string {
  if (minify) {
    return JSON.stringify(data);
  } else {
    return JSON.stringify(data, null, 2);
  }
}

// For APIs, minified is usually the default (smaller payload)
function formatResponse(data: any, minify: boolean = true): string {
  // ... implementation
}

Example 3: Config File Writer
function saveConfig(config: any, pretty: boolean = true): string {
  // Users usually want readable config files
  if (pretty) {
    return JSON.stringify(config, null, 2);
  } else {
    return JSON.stringify(config);
  }
}

// Save to file
const configString = saveConfig({ debug: true, port: 3000 });
fs.writeFileSync("config.json", configString);

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TESTING & VERIFICATION:
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interface TestData {
  name: string;
  value: number;
}

const testObj: TestData = {
  name: "test",
  value: 42
};

// Test 1: Pretty format
const pretty = convertToJSON(testObj, true);
console.log("Test 1 (Pretty):");
console.log(pretty);
console.log("Contains newlines:", pretty.includes("\n"));
console.log("Matches regex:", /{\n\s+/.test(pretty));

// Test 2: Compact format (explicit false)
const compact = convertToJSON(testObj, false);
console.log("\nTest 2 (Compact - explicit false):");
console.log(compact);
console.log("Contains newlines:", compact.includes("\n"));

// Test 3: Compact format (default)
const default_ = convertToJSON(testObj);
console.log("\nTest 3 (Compact - default):");
console.log(default_);
console.log("Compact and default are same:", compact === default_);

// Test 4: Parse back and verify
const parsed = JSON.parse(pretty);
console.log("\nTest 4 (Round-trip):");
console.log("Parsed correctly:", parsed.name === "test" && parsed.value === 42);

// Test 5: Nested objects
const nested = {
  user: { id: 1, name: "Alice" },
  posts: [
    { id: 1, title: "Post 1" },
    { id: 2, title: "Post 2" }
  ]
};

console.log("\nTest 5 (Nested objects):");
console.log("Pretty:");
console.log(convertToJSON(nested, true));
console.log("\nCompact:");
console.log(convertToJSON(nested, false));

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KEY TAKEAWAYS:
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✅ Overloads can represent different behavior based on parameters
✅ JSON.stringify with null and indent number creates pretty JSON
✅ Default parameters make functions more convenient to use
✅ Boolean parameter with overloads is a common pattern
✅ Consider whether a boolean or options object is clearer
✅ Overloads help users understand what the function can do

Pattern Summary:
- format: true → pretty/verbose output
- format: false/undefined → compact output
- This pattern appears in many APIs (prettier, logger, etc.)

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