var accounts = [
  { name: 'James Brown', msgCount: 123 },
  { name: 'Stevie Wonder', msgCount: 22 },
  { name: 'Sly Stone', msgCount: 16 },
  { name: 'Otis Redding', msgCount: 300 }  // Otis has the most messages
];

// get sum of msgCount prop across all objects in array
var msgTotal = accounts.reduce(function(prev, cur) {
  return prev + cur.msgCount;
}, 0);

console.log('Total Messages:', msgTotal); // Total Messages: 461