Order changed by updateIn

[jeff303]

Consider the following snippet, run against Icepick 2.4.0:

var icepick = require("icepick")

const BEFORE = {
  first: {
    name: "First",
    items: [{key: "first-a", value: 12}]
  },
  second: {
    name: "Second",
    items: [{key: "second-a", value: 13}]
  },
  third: {
    name: "Third",
    items: [{key: "third-a", value: 15}]
  }
};

console.log(BEFORE);

const AFTER = icepick.updateIn(BEFORE, ["second", "items"], items => [
  ...items,
  {
    key: "second-x",
    value: 42
  },
]);

console.log(AFTER);

In this case, the output is:

Object
first: Object {name: "First", items: [Object {key: "first-a", value: 12}]}
second: Object {name: "Second", items: [Object {key: "second-a", value: 13}]}
third: Object {name: "Third", items: [Object {key: "third-a", value: 15}]}

Object
third: Object {name: "Third", items: [Object {key: "third-a", value: 15}]}
second: Object {items: [Object {key: "second-a", value: 13}, Object {key: "second-x", value: 42}], name: "Second"}
first: Object {name: "First", items: [Object {key: "first-a", value: 12}]}

Notice that the order of keys has been reversed by this operation (where an item was added to the items collection of the 2nd value in the map). I realize that maps are inherently unordered, but it might still be useful if this operation didn't change the order.