mutability1.js

var someGreeting = "hello";
var otherGreeting = someGreeting;

console.log(someGreeting);              // Logs: hello
console.log(otherGreeting);             // Logs: hello

someGreeting.concat("!!!");
  // return value: "hello!!!"

console.log(someGreeting);              // Logs: hello
console.log(otherGreeting);             // Logs: hello

console.log(someGreeting[1]);           // Logs: e
someGreeting[1] = "a";
console.log(someGreeting[1]);           // Logs: e

someGreeting = someGreeting.concat("!!!");
  // reassignment

console.log(someGreeting);              // Logs: hello!!!
console.log(otherGreeting);             // Logs: hello