gistfile1.txt

let realmItems = nextProps.items || []
let start = new Date()
let finish = new Date()
let a = []

// items.length = 479
for (let i = 0, len = realmItems.length; i < len; ++i) {
  // Option A
  a.push({name: 'item_name' + Math.round(Math.random() * 100), category: {name: 'category_name ' + i, image: 'image_name'}})

  // Option B (accessing an object attribute)
  // a.push({name: realmItems[i].name, category: {name: 'category_name ' + i, image: 'image_name'}})
}

finish = new Date()

var dif = (finish.getTime() - start.getTime()) / (1000)

// Option A is 0.05 seconds
// Option B is ~4.66 seconds
console.log(dif, 'seconds')