elements-kinds

JS helper function to debug elements kinds in v8

More details in this blogpost by Mathias Bynes

DISCLAMIER: This module is not 100% correct, Its just a reference implementation in JavaScript.

Any JS only implementation can only guess what the elements kind is. The proper way of finding out is to get the debug build of d8 and in the REPL use the special %DebugPrint(object) function.

$ out.gn/x64.debug/d8 --allow-natives-syntax
d8> const array = [1, 2, 3]; %DebugPrint(array);
DebugPrint: 0x1fbbad30fd71: [JSArray]
 - map = 0x10a6f8a038b1 [FastProperties]
 - prototype = 0x1212bb687ec1
 - elements = 0x1fbbad30fd19 <FixedArray[3]> [PACKED_SMI_ELEMENTS (COW)]
 - length = 3
 - properties = 0x219eb0702241 <FixedArray[0]> {
    #length: 0x219eb0764ac9 <AccessorInfo> (const accessor descriptor)
 }
 - elements= 0x1fbbad30fd19 <FixedArray[3]> {
           0: 1
           1: 2
           2: 3
 }

Installation

yarn add elements-kinds
// npm
npm install elements-kinds

Usage

const getElementsKinds = require("elements-kinds");
console.log(getElementsKinds(new Array(12));
// HOLEY_SMI_ELEMENTS
console.log(getElementsKinds([1, 2, "1", "3", 1.21]));
// PACKED_ELEMENTS