7.1 Counter created by smillaraaq - https://repl.it/HHjJ/1

7.1 Counter.js

var counter = 0;

function increment(num){
  counter += num;
  console.log("counter: " + counter);
}

increment(2);    // counter is now 2
increment(6);    // counter is now 8
increment(-1);    // counter is now 7