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1.1.4 • Public • Published

Hyperjump - Browser

The Hyperjump Browser is a generic client for traversing JSON Reference (JRef) and other JRef-compatible media types in a way that abstracts the references without loosing information.


This module is designed for node.js (ES Modules, TypeScript) and browsers. It should work in Bun and Deno as well, but the test runner doesn't work in these environments, so this module may be less stable in those environments.


npm install @hyperjump/browser

JRef Browser

This example uses the API at https://swapi.hyperjump.io. It's a variation of the Star Wars API (SWAPI) implemented using the JRef media type.

import { get, step, value, iter } from "@hyperjump/browser";

const aNewHope = await get("https://swapi.hyperjump.io/api/films/1");
const characters = await get("#/characters", aNewHope); // Or
const characters = await step("characters", aNewHope);

for await (const character of iter(characters)) {
  const name = await step("name", character);
  value(name); // => Luke Skywalker, etc.

You can also work with files on the file system. When working with files, media types are determined by file extensions. The JRef media type uses the .jref extension.

import { get, value } from "@hyperjump/browser";

const lukeSkywalker = await get("./api/people/1.jref"); // Paths resolve relative to the current working directory
const name = await step("name", lukeSkywalker);
value(name); // => Luke Skywalker


  • get(uri: string, browser?: Browser): Promise<Browser>

    Retrieve a document located at the given URI. Support for JRef is built in. See the Media Types section for information on how to support other media types. Support for http(s): and file: URI schemes are built in. See the Uri Schemes section for information on how to support other URI schemes.

  • value(browser: Browser) => JRef

    Get the JRef compatible value the document represents.

  • typeOf(browser: Browser) => JRefType

    Works the same as the typeof keyword. It will return one of the JSON types (null, boolean, number, string, array, object) or "reference". If the value is not one of these types, it will throw an error.

  • has(key: string, browser: Browser) => boolean

    Returns whether or not a property is present in the object that the browser represents.

  • length(browser: Browser) => number

    Get the length of the array that the browser represents.

  • step(key: string | number, browser: Browser) => Promise<Browser>

    Move the browser cursor by the given "key" value. This is analogous to indexing into an object or array (foo[key]). This function supports curried application.

  • iter(browser: Browser) => AsyncGenerator<Browser>

    Iterate over the items in the array that the document represents.

  • entries(browser: Browser) => AsyncGenerator<[string, Browser]>

    Similar to Object.entries, but yields Browsers for values.

  • values(browser: Browser) => AsyncGenerator<Browser>

    Similar to Object.values, but yields Browsers for values.

  • keys(browser: Browser) => Generator<string>

    Similar to Object.keys.

Media Types

Support for the JRef media type is included by default, but you can add support for any media type you like as long as it can be represented in a JRef-compatible way.

import { addMediaTypePlugin, removeMediaTypePlugin, setMediaTypeQuality } from "@hyperjump/browser";
import YAML from "yaml";

// Add support for YAML version of JRef (YRef)
addMediaTypePlugin("application/reference+yaml", {
  parse: async (response) => {
    return {
      baseUri: response.url,
      root: (response) => YAML.parse(await response.text(), (key, value) => {
        return value !== null && typeof value.$ref === "string"
          ? new Reference(value.$ref)
          : value;
      anchorLocation: (fragment) => decodeUri(fragment ?? "");
  fileMatcher: (path) => path.endsWith(".jref")

// Prefer "YRef" over JRef by reducing the quality for JRef.
setMediaTypeQuality("application/reference+json", 0.9);

// Only support YRef by removing JRef support.


  • addMediaTypePlugin(contentType: string, plugin: MediaTypePlugin): void

    Add support for additional media types.

    • type MediaTypePlugin
      • parse: (response: Response) => Document
      • quality: number (defaults to 1)
  • removeMediaTypePlugin(contentType: string): void

    Removed support or a media type.

  • setMediaTypeQuality(contentType: string, quality: number): void;

    Set the quality that will be used in the Accept header of requests to indicate to servers what media types are preferred over others.

  • acceptableMediaTypes(): string;

    Build an Accept request header from the registered media type plugins. This function is used internally. You would only need it if you're writing a custom http(s): URI scheme plugin.

URI Schemes

By default, http(s): and file: URIs are supported. You can add support for additional URI schemes using plugins.

import { addUriSchemePlugin, removeUriSchemePlugin, retrieve } from "@hyperjump/browser";

// Add support for the `urn:` scheme
addUriSchemePlugin("urn", {
  parse: (urn, baseUri) => {
    let { nid, nss, query, fragment } = parseUrn(urn);
    nid = nid.toLowerCase();

    if (!mappings[nid]?.[nss]) {
      throw Error(`Not Found -- ${urn}`);

    let uri = mappings[nid][nss];
    uri += query ? "?" + query : "";
    uri += fragment ? "#" + fragment : "";

    return retrieve(uri, baseUri);

// Only support `urn:` by removing default plugins


  • addUriSchemePlugin(scheme: string, plugin: UriSchemePlugin): void

    Add support for additional URI schemes.

    • type UriSchemePlugin
      • retrieve: (uri: string, baseUri?: string) => Promise<Response>
  • removeUriSchemePlugin(scheme: string): void

    Remove support for a URI scheme.

  • retrieve(uri: string, baseUri?: string) => Promise<Response>

    This is used internally, but you may need it if mapping names to locators such as in the example above.


parse and stringify JRef values using the same API as the JSON built-in functions including reviver and replacer functions.

import { parse, stringify, jrefTypeOf } from "@hyperjump/browser/jref";

const blogPostJref = `{
  "title": "Working with JRef",
  "author": { "$ref": "/author/jdesrosiers" },
  "content": "lorem ipsum dolor sit amet",
const blogPost = parse(blogPostJref);
jrefTypeOf(blogPost.author) // => "reference"
blogPost.author.href; // => "/author/jdesrosiers"

stringify(blogPost, null, "  ") === blogPostJref // => true


export type Replacer = (key: string, value: unknown) => unknown;

  • parse: (jref: string, reviver?: (key: string, value: unknown) => unknown) => JRef;

    Same as JSON.parse, but converts { "$ref": "..." } to Reference objects.

  • stringify: (value: JRef, replacer?: (string | number)[] | null | Replacer, space?: string | number) => string;

    Same as JSON.stringify, but converts Reference objects to { "$ref": "... " }

  • jrefTypeOf: (value: unknown) => "object" | "array" | "string" | "number" | "boolean" | "null" | "reference" | "undefined";



Run the tests

npm test

Run the tests with a continuous test runner

npm test -- --watch

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