Example function in JavaScript

pigdog.js

function mergeTwoNamesIntoOneWithoutSpaces(speciesOne, speciesTwo) {
  // speciesOne and speciesTwo are variables; by defining what happens to the
  // variables in a function, it lets us transform anything (of a compatible data type) 
  // that we pass into the function
  
  // whatever we "return" is what the function spits out
  return speciesOne + speciesTwo;
  
}

var animalOne = "Pig";
var animalTwo = "Dog";
var animalThree = mergeTwoNamesIntoOneWithoutSpaces(animalOne, animalTwo); // animalThree should be "PigDog"