JSPM

UserUtils

Library with various utilities for userscripts - register listeners for when CSS selectors exist, intercept events, modify the DOM more easily and more.
Contains builtin TypeScript declarations.

Table of Contents:

• Installation
• Features
  • onSelector() - call a listener once a selector is found in the DOM
  • initOnSelector() - needs to be called once to be able to use onSelector()
  • autoPlural() - automatically pluralize a string
  • clamp() - clamp a number between a min and max value
  • pauseFor() - pause the execution of a function for a given amount of time
  • debounce() - call a function only once, after a given amount of time
  • getUnsafeWindow() - get the unsafeWindow object or fall back to the regular window object
  • insertAfter() - insert an element as a sibling after another element
  • addParent() - add a parent element around another element
  • addGlobalStyle() - add a global style to the page
  • preloadImages() - preload images into the browser cache for faster loading later on
  • fetchAdvanced() - wrapper around the fetch API with a timeout option
  • openInNewTab() - open a link in a new tab
  • interceptEvent() - conditionally intercepts events registered by addEventListener() on any given EventTarget object
  • interceptWindowEvent() - conditionally intercepts events registered by addEventListener() on the window object
• License

Installation:

• If you are using a bundler like webpack, you can install this package using npm:

  npm i @sv443-network/userutils

  Then, import it in your script as usual:

  import { addGlobalStyle } from "@sv443-network/userutils";
  // or
  import * as userUtils from "@sv443-network/userutils";

  Shameless plug: I also have a webpack-based template for userscripts in TypeScript that you can use to get started quickly.

• If you are not using a bundler, you can include the latest release from GreasyFork by adding this directive to the userscript header:

  // @require https://greasyfork.org/scripts/TODO

If you like using this library, please consider supporting development

Features:

onSelector()

Usage:

onSelector<TElement = HTMLElement>(selector: string, options: {
  listener: (elements: TElement | NodeListOf<TElement>) => void,
  all?: boolean,
  continuous?: boolean,
}): void

Registers a listener to be called whenever the element(s) behind a selector is/are found in the DOM.
If the selector already exists, the listener will be called immediately.

If all is set to true, querySelectorAll() will be used instead and the listener will return a NodeList of matching elements.
This will also include elements that were already found in a previous listener call.
If set to false (default), querySelector() will be used and only the first element will be returned.

If continuous is set to true, the listener will not be deregistered after it was called once (defaults to false).

When using TypeScript, the generic TElement can be used to specify the type of the element(s) that the listener will return.

⚠️ In order to use this function, initOnSelector() has to be called as soon as possible.
This initialization function has to be called after DOMContentLoaded is fired (or immediately if @run-at document-end is set).

Calling onSelector() before DOMContentLoaded is fired will not throw an error, but it also won't trigger listeners until the DOM is accessible.

document.addEventListener("DOMContentLoaded", initOnSelector);

// Continuously checks if `div` elements are added to the DOM, then returns all of them (even previously detected ones) in a NodeList
onSelector("div", {
  listener: (element) => {
    console.log("Elements found:", element);
  },
  all: true,
  continuous: true,
});

// Checks if an input element with a value attribute of "5" is added to the DOM, then returns it and deregisters the listener
onSelector("input[value=\"5\"]", {
  listener: (element) => {
    console.log("Element found:", element);
  },
});

initOnSelector()

Usage:

initOnSelector(options: {
  attributes?: boolean,
  characterData?: boolean,
}): void

Initializes the MutationObserver that is used by onSelector() to check for the registered selectors whenever a DOM change occurs on the <body>
By default, this only checks if elements are added or removed (at any depth).

Set attributes to true to also check for attribute changes on every single descendant of the <body> (defaults to false).
Set characterData to true to also check for character data changes on every single descendant of the <body> (defaults to false).

⚠️ Using these extra options can have a performance impact on larger sites or sites with a constantly changing DOM.

⚠️ This function needs to be run after the DOM has loaded (when using @run-at document-end or after DOMContentLoaded has fired).

document.addEventListener("DOMContentLoaded", () => {
  initOnSelector({
    attributes: true,
    characterData: true,
  });
});

autoPlural()

Usage: autoPlural(str: string, num: number | Array | NodeList): string

Automatically pluralizes a string if the given number is not 1.
If an array or NodeList is passed, the length of it will be used.

autoPlural("apple", 0); // "apples"
autoPlural("apple", 1); // "apple"
autoPlural("apple", 2); // "apples"

autoPlural("apple", [1]);    // "apple"
autoPlural("apple", [1, 2]); // "apples"

clamp()

Usage: clamp(num: number, min: number, max: number): number

Clamps a number between a min and max value.

clamp(5, 0, 10);        // 5
clamp(-1, 0, 10);       // 0
clamp(Infinity, 0, 10); // 10

pauseFor()

Usage: pauseFor(ms: number): Promise<void>

Pauses async execution for a given amount of time.

async function run() {
  console.log("Hello");
  await pauseFor(3000); // waits for 3 seconds
  console.log("World");
}

debounce()

Usage: debounce(func: Function, timeout?: number): Function

Debounces a function, meaning that it will only be called once after a given amount of time.
This is very useful for functions that are called repeatedly, like event listeners, to remove extraneous calls.
The timeout will default to 300ms if left undefined.

window.addEventListener("resize", debounce((event) => {
  console.log("Window was resized:", event);
}, 500)); // 500ms timeout

getUnsafeWindow()

Usage: getUnsafeWindow(): Window

Returns the unsafeWindow object or falls back to the regular window object if the @grant unsafeWindow is not given.
Userscripts are sandboxed and do not have access to the regular window object, so this function is useful for websites that reject some events that were dispatched by the userscript.

const mouseEvent = new MouseEvent("click", {
  view: getUnsafeWindow(),
});
document.body.dispatchEvent(mouseEvent);

insertAfter()

Usage: insertAfter(beforeElement: HTMLElement, afterElement: HTMLElement): HTMLElement

Inserts the element passed as afterElement as a sibling after the passed beforeElement.
The passed afterElement will be returned.

⚠️ This function needs to be run after the DOM has loaded (when using @run-at document-end or after DOMContentLoaded has fired).

const beforeElement = document.querySelector("#before");
const afterElement = document.createElement("div");
afterElement.innerText = "After";
insertAfter(beforeElement, afterElement);

addParent()

Usage: addParent(element: HTMLElement, newParent: HTMLElement): HTMLElement

Adds a parent element around the passed element and returns the new parent.
Previously registered event listeners are kept intact.

⚠️ This function needs to be run after the DOM has loaded (when using @run-at document-end or after DOMContentLoaded has fired).

const element = document.querySelector("#element");
const newParent = document.createElement("a");
newParent.href = "https://example.org/";
addParent(element, newParent);

addGlobalStyle()

Usage: addGlobalStyle(css: string): void

Adds a global style to the page in form of a <style> element that's inserted into the <head>.
⚠️ This function needs to be run after the DOM has loaded (when using @run-at document-end or after DOMContentLoaded has fired).

document.addEventListener("DOMContentLoaded", () => {
  addGlobalStyle(`
    body {
      background-color: red;
    }
  `);
});

preloadImages()

Usage: preloadImages(urls: string[], rejects?: boolean): Promise<void>

Preloads images into browser cache by creating an invisible <img> element for each URL passed.
The images will be loaded in parallel and the returned Promise will only resolve once all images have been loaded.
The resulting PromiseSettledResult array will contain the image elements if resolved, or an ErrorEvent if rejected, but only if rejects is set to true.

preloadImages([
  "https://example.org/image1.png",
  "https://example.org/image2.png",
  "https://example.org/image3.png",
], true)
  .then((results) => {
    console.log("Images preloaded. Results:", results);
  });

fetchAdvanced()

Usage:

fetchAdvanced(url: string, options?: {
  timeout?: number,
  // any other options from fetch() except for signal
}): Promise<Response>

A wrapper around the native fetch() function that adds options like a timeout property.
The timeout will default to 10 seconds if left undefined.

fetchAdvanced("https://api.example.org/data", {
  timeout: 5000,
  headers: {
    "Accept": "application/json",
  },
}).then(async (response) => {
  console.log("Data:", await response.json());
});

openInNewTab()

Usage: openInNewTab(url: string): void

Creates an invisible anchor with a _blank target and clicks it.
Contrary to window.open(), this has a lesser chance to get blocked by the browser's popup blocker and doesn't open the URL as a new window.
This function has to be run in relatively quick succession in response to a user interaction event, else the browser might reject it.

⚠️ This function needs to be run after the DOM has loaded (when using @run-at document-end or after DOMContentLoaded has fired).

document.querySelector("#button").addEventListener("click", () => {
  openInNewTab("https://example.org/");
});

interceptEvent()

Usage: interceptEvent(eventObject: EventTarget, eventName: string, predicate: () => boolean): void

Intercepts all events dispatched on the eventObject and prevents the listeners from being called as long as the predicate function returns a truthy value.
Calling this function will set the Error.stackTraceLimit to 1000 to ensure the stack trace is preserved.

⚠️ This function should be called as soon as possible (I recommend using @run-at document-start), as it will only intercept events that are attached after this function is called.

interceptEvent(document.body, "click", () => {
  return true; // prevent all click events on the body
});

interceptWindowEvent()

Usage: interceptWindowEvent(eventName: string, predicate: () => boolean): void

Intercepts all events dispatched on the window object and prevents the listeners from being called as long as the predicate function returns a truthy value.
This is essentially the same as interceptEvent(), but automatically uses the unsafeWindow (or falls back to regular window).

⚠️ This function should be called as soon as possible (I recommend using @run-at document-start), as it will only intercept events that are attached after this function is called.

interceptWindowEvent("beforeunload", () => {
  return true; // prevent the pesky "Are you sure you want to leave this page?" popup
});

License:

This library is licensed under the MIT License.
See the license file for details.