W3Schools Tryit Editor

// Function Return Type Inference
// In TypeScript, return types would be inferred automatically

// Function with string return type
function greet(name) {
  return `Hello, ${name}!`;
}

// Function with number return type
function add(a, b) {
  return a + b;
}

// Function that returns different types based on input
function getValue(key) {
  if (key === "name") {
    return "Alice";
  } else {
    return 42;
  }
}

// Using the functions and showing their return types
console.log("greet function:");
const greeting = greet("Bob");
console.log("Return value:", greeting);
console.log("Return type:", typeof greeting);
console.log("");

console.log("add function:");
const sum = add(5, 3);
console.log("Return value:", sum);
console.log("Return type:", typeof sum);
console.log("");

console.log("getValue function with key='name':");
const value1 = getValue("name");
console.log("Return value:", value1);
console.log("Return type:", typeof value1);
console.log("");

console.log("getValue function with key='age':");
const value2 = getValue("age");
console.log("Return value:", value2);
console.log("Return type:", typeof value2);
console.log("");

console.log("In TypeScript, getValue would have a return type of 'string | number'");

greet function:
Return value: Hello, Bob!
Return type: string

add function:
Return value: 8
Return type: number

getValue function with key='name':
Return value: Alice
Return type: string

getValue function with key='age':
Return value: 42
Return type: number

In TypeScript, getValue would have a return type of 'string | number'