Elements Kinds
https://v8project.blogspot.com/2017/09/elements-kinds-in-v8.html
Elements Kinds are type of content of array. Depending on what kind of elements they are, the way to optimize is different. Elements Kinds could not be upgraded but only downgraded. Holey elements kinds are slower than packed ones so that best practice is keeping elements packed into array.
| Name | Element Types in array | Has Space? |
|---|---|---|
| PACKED_SMI_ELEMENTS | Integer | NO |
| HOLEY_SMI_ELEMENTS | Integer | YES |
| PACKED_DOUBLE_ELEMENTS | Double | NO |
| HOLEY_DOUBLE_ELEMENTS | Double | YES |
| PACKED_ELEMENTS | Any | NO |
| HOLEY_ELEMENTS | Any | YES |
var array = new Array(10);