function outer(greeting, msg = "It's a fine day to learn") {
  // 2
  const innerFunction = function (name, lang = "Python") {
    // 3
    return `${greeting}, ${name}! ${msg} ${lang}`; // 4
  };
  return innerFunction("student", "JavaScript"); // 5
}

outer("Hello"); // 1
//=> "Hello, student! It's a fine day to learn JavaScript"

function outer(greeting, msg = "It's a fine day to learn") {
  return function (name, lang = "Python") {
    return `${greeting}, ${name}! ${msg} ${lang}`;
  };
}

outer("Hello")("student", "JavaScript");
//=> "Hello, student! It's a fine day to learn JavaScript"