json-in-order v0.2.1

json-in-order

Like JSON.parse, but preserving the key order from JSON objects; wherever JSON.parse produces a plain object, it produces a Map.

Usage

import {parse} from 'json-in-order';

const json = '{"2":"hearts","1":"soul"}';
const m = parse(json);

console.log(m.constructor.name);   // Map
console.log([...m].join(' / '));   // 2,hearts / 1,soul

Motivation

Since ES2015, JavaScript object keys have a well-defined order for iteration. This is almost the order in which they were inserted, but not quite. In particular, the keys "2" and "1" from the above example are returned in a different order if you put them in an object:

const obj = {"2":"hearts"};
obj["1"]="soul";
console.log(Object.entries(obj).join(' / '));  // 1,soul / 2,hearts

This means that if you're parsing JSON, and are interested in the order in which the keys appear in the input string, you cannot use JSON.parse - because it will always construct an object. In which, by the way, it is totally justified, because objects have no defined order in the JSON spec.

Still, object keys do have an order in the JSON string, and who is Douglas Crockford to say that you must ignore it? ES2015 also introduced a standard Map datatype whose iteration order does follow the exact insertion order. The package you are looking at parses JSON objects as a Map instead of an object. Use it as you see fit.

Credits

Actual parsing is performed by clarinet.