sum_without_highest_lowest.js

const sumArray = (a) => {
  if ( typeof a == 'undefined' || !a || a.length < 2 ) { return 0; }
  
  a.sort((a,b) => a - b).splice(0, 1)
  a.splice(a.length - 1, 1);
  
  if ( a.length < 3 ) { return 0; }
  
  return a.reduce((a,b) => a+b);
};