// 1. FUNCTION CONSTRUCTOR
var multiply = new Function("x", "y", "return x * y;");

// 2. FUNCTION DECLARATION
function multiply(x, y) {
  return x * y;
}

// 3. FUNCTION EXPRESSION
var multiply = function (x, y) {
  return x * y;
};

// 4. NAMED FUNCTION EXPRESSION
var multiply = function func_name(x, y) {
  return x * y;
};