node-d3-collection 1.0.4-2 (amd64 binary) in ubuntu bionic

 A common data type in JavaScript is the *associative array*, or more simply
 the *object*, which has a set of named properties. The standard mechanism for
 iterating over the keys (or property names) in an associative array is the
 for…in loop. However, note that the iteration order is undefined.
 .
 D3 provides several methods for converting associative arrays to standard
 arrays with numeric indexes.
 .
 Node.js is an event-based server-side JavaScript engine.