ES2015 - Proxy - Dynamic properties (all*, any*) in Array

gistfile1.js

/**
 * Proxy an Array - add all* property to filter by object predicate, and any* to emulate underscore some/any
 * 
 * For example: proxy an array of objects, having some Boolean values on each of them
 * following the is* predicate form. We'll then trap get calls, to return allXXX (sub array) or to 
 * query anyXXX (Boolean)
 * 
 */
let Users = new Proxy([
  { id: 1, username: 'Charlie', isAdmin: true, isRobot: false },
  { id: 2, username: 'Johnny-Five', isAdmin: false, isRobot: true },
  { id: 3, username: 'Sgt. Pepper', isAdmin: false, isRobot: false },
  { id: 4, username: 'Replicant', isAdmin: true, isRobot: true }
],
{
  get(obj, prop){
    if(prop.indexOf('all') === 0){
      return this.getAll(obj, prop);
    }
    if(prop.indexOf('any') === 0){
      return this.getAny(obj, prop);
    }
    return obj[prop];
  },
  getAll(obj, prop){
    //find key with that name
    let key = prop.replace('all', '');
    //handle plural names
    if(key.endsWith('s')){
      key = key.substr(0, key.length-1);
    }
    return obj.filter(item => item['is' + key] === true);
  },
  getAny(obj,prop){
    let key = prop.replace('any', '');
    if(key.endsWith('s'))
      key = key.substr(0, key.length-1);
    return obj.filter(item => item['is' + key] === true).length > 0
  }
});

console.log(Users.allRobot);
console.log(Users.anyAdmin);
console.log(Users.anyDrunk);

Only works in Firefox / MS Edge as of today