Functions As Values

JavaScript supports first-class and higher-order functions, which are just fancy ways of saying "functions as values". Functions can be treated like any other data type—such as numbers and strings and booleans. Let's assume we have two simple functions:

function add(x, y) {
  return x + y;
}

function mul(x, y) {
  return x * y;
}

We can create a new aggregate function that accepts a function as its 4th argument:

function aggregate(a, b, c, arithmetic) {
  const firstResult = arithmetic(a, b);
  const secondResult = arithmetic(firstResult, c);
  return secondResult;
}

It calls the given arithmetic function (which could be add or mul, or any other function that accepts two parameters and returns a number) and applies it to three inputs instead of two. It can be used like this:

function main() {
  const sum = aggregate(2, 3, 4, add);
  // sum is 9
  const product = aggregate(2, 3, 4, mul);
  // product is 24
}

Assignment

Complete the reformat function. It takes a message string and a formatter function as input:

Apply the given formatter three times to the message
Add a prefix of TEXTIO: to the result
Return the final string

For example, if the message is "General Kenobi" and the formatter adds a period to the end of the string, the final result should be:

TEXTIO: General Kenobi...