Advanced JS stuff

advanced.js

// Tell me what is going on here:
function oneHitter(name, val){
  if(!oneHitter.cache) oneHitter.cache = {};
  if(!oneHitter.cache[name]) oneHitter.cache[name] = val
  return oneHitter.cache[name];
}

// Tell me what's going on here':
var days = ["sun","mon","tues","wed","thurs","fri","sat"];
function lastElement(arr){
  return arr.splice(arr.length -1);
}
var lastDay = lastElement(days);
days.concat(lastDay).length === 8; // <- what does this evaluate to and why?