[cmpolis]

this is a great way to store structured data in js since it saves the memory cost having repeated keys. e.g.:

  records = {
    time: [1000, 1001],
    price: [20, 25],
    volume: [50, 15]  
  }

  records = [
      { time: 1000, price: 20, volume: 50 },
      { time: 1001, price: 25, volume: 15 }
  ]
  // not a big difference with 2 records, but for xxxx records...

[hayley-patton]

Decent JS engines will use "hidden classes" to dedupe keys for you already, so this isn't necessary to save space; the technique is pretty old and dates to Self. Still, the arrangement may help with locality of reference.

[dan-robertson]

In practice, most js engines these days can ‘recognise’ the ‘class’ of these objects (if you create them from scratch in a few places) and the memory representation would end up with a word for the ‘class’ which says that time is at field 0 and price at 1 and volume at 2, and then the data itself. The main reason is to speed up code that reads the fields rather than memory use.