UserUtils

Zero-dependency 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. Webpack compatible and supports ESM and CJS.
If you like using this library, please consider supporting the development ❤️

Installation
Preamble
License
Features
- DOM:
  - onSelector() - call a listener once a selector is found in the DOM
  - initOnSelector() - needs to be called once to be able to use onSelector()
  - getSelectorMap() - returns all currently registered selectors, listeners and options
  - 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
  - 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
  - amplifyMedia() - amplify an audio or video element's volume past the maximum of 100%
- Math:
  - clamp() - constrain a number between a min and max value
  - mapRange() - map a number from one range to the same spot in another range
  - randRange() - generate a random number between a min and max boundary
- Misc:
  - autoPlural() - automatically pluralize a string
  - 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
  - fetchAdvanced() - wrapper around the fetch API with a timeout option
- Arrays:
  - randomItem() - returns a random item from an array
  - randomItemIndex() - returns a tuple of a random item and its index from an array
  - takeRandomItem() - returns a random item from an array and mutates it to remove the item
  - randomizeArray() - returns a copy of the array with its items in a random order

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/472956-userutils/code/UserUtils.js

Then, access the functions on the global variable UserUtils:

UserUtils.addGlobalStyle("body { background-color: red; }");

// or using object destructuring:

const { clamp } = UserUtils;
console.log(clamp(1, 5, 10); // 5

Preamble:

This library is written in TypeScript and contains builtin TypeScript declarations.
The usages and examples in this readme are written in TypeScript, but the library can also be used in plain JavaScript.

Some functions require the @run-at or @grant directives to be tweaked in the userscript header or have other requirements.
Their documentation will contain a section marked by a warning emoji (⚠️) that will go into more detail.

If the usage contains multiple definitions of the function, each line represents an overload and you can choose which one you want to use.

License:

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

Features:

DOM:

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 matching 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.

Example - click to view

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<HTMLDivElement>("div", {
  listener: (elements) => {
    console.log("Elements found:", elements); // type = NodeListOf<HTMLDivElement>
  },
  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<HTMLInputElement>("input[value=\"5\"]", {
  listener: (element) => {
    console.log("Element found:", element); // type = HTMLInputElement
  },
});

initOnSelector()

Usage:

initOnSelector(options?: MutationObserverInit): 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).

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

The options object is passed directly to the MutationObserver.observe() method.
Note that options.subtree and options.childList will be set to true by default.
You may see all options here, but these are the important ones:

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

Example - click to view

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

getSelectorMap()

Usage: getSelectorMap(): Map<string, OnSelectorOptions[]>

Returns a Map of all currently registered selectors and their options, including listener function.
Since multiple listeners can be registered for the same selector, the value of the Map is an array of OnSelectorOptions objects.

Example - click to view

document.addEventListener("DOMContentLoaded", initOnSelector);

onSelector<HTMLDivElement>("div", {
  listener: (elements) => void 0,
  all: true,
  continuous: true,
});

onSelector<HTMLDivElement>("div", {
  listener: (elements) => void 0,
});

const selectorMap = getSelectorMap();
// Map(1) {
//   "div" => [
//     {
//       listener: (elements) => void 0,
//       all: true,
//       continuous: true,
//     },
//     {
//       listener: (elements) => void 0,
//     },
//   ]
// }

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.

Example - click to view

// trick the site into thinking the mouse was moved:
const mouseEvent = new MouseEvent("mousemove", {
  view: getUnsafeWindow(),
  screenY: 69,
  screenX: 420,
  movementX: 10,
  movementY: 0,
});
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).

Example - click to view

// insert a <div> as a sibling next to an element
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).

Example - click to view

// add an <a> around an element
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).

Example - click to view

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.

Example - click to view

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);
  });

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 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).

Example - click to view

document.querySelector("#my-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 (if it's not already higher) 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.

Example - click to view

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

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.

Example - click to view

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

amplifyMedia()

Usage: amplifyMedia(mediaElement: HTMLMediaElement, multiplier?: number): AmplifyMediaResult

Amplifies the gain of a media element (like <audio> or <video>) by a given multiplier (defaults to 1.0).
This is how you can increase the volume of a media element beyond the default maximum volume of 1.0 or 100%.
Make sure to limit the multiplier to a reasonable value (clamp() is good for this), as it may cause clipping or bleeding eardrums.

⚠️ This function has to be run in response to a user interaction event, else the browser will reject it because of the strict autoplay policy.

Returns an object with the following properties:

Property	Description
`mediaElement`	The passed media element
`amplify()`	A function to change the amplification level
`getAmpLevel()`	A function to return the current amplification level
`context`	The AudioContext instance
`source`	The MediaElementSourceNode instance
`gain`	The GainNode instance

Example - click to view

const audio = document.querySelector<HTMLAudioElement>("audio");
const button = document.querySelector<HTMLButtonElement>("button");

// amplifyMedia needs to be called in response to a user interaction event:
button.addEventListener("click", () => {
  const { amplify, getAmpLevel } = amplifyMedia(audio);

  const setGain = (value: number) => {
    // constrain the value to between 0 and 5
    amplify(clamp(value, 0, 5));
    console.log("Gain set to", getAmpLevel());
  }

  setGain(2);    // set gain to 2x
  setGain(3.5);  // set gain to 3.5x

  console.log(getAmpLevel()); // 3.5
});

Math:

clamp()

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

Clamps a number between a min and max value.

Example - click to view

clamp(5, 0, 10);        // 5
clamp(-1, 0, 10);       // 0
clamp(7, 0, 10);        // 7
clamp(Infinity, 0, 10); // 10

mapRange()

Usage: mapRange(value: number, range_1_min: number, range_1_max: number, range_2_min: number, range_2_max: number): number

Maps a number from one range to the spot it would be in another range.

Example - click to view

mapRange(5, 0, 10, 0, 100); // 50
mapRange(5, 0, 10, 0, 50);  // 25
// to calculate a percentage from arbitrary values, use 0 and 100 as the second range:
mapRange(4, 0, 13, 0, 100); // 30.76923076923077

randRange()

Usages:

randRange(min: number, max: number): number
randRange(max: number): number

Returns a random number between min and max (inclusive).
If only one argument is passed, it will be used as the max value and min will be set to 0.

Example - click to view

randRange(0, 10);  // 4
randRange(10, 20); // 17
randRange(10);     // 7

Misc:

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.

Example - click to view

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

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

const items = [1, 2, 3, 4, "foo", "bar"];
console.log(`Found ${items.length} ${autoPlural("item", items)}`); // "Found 6 items"

pauseFor()

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

Pauses async execution for a given amount of time.

Example - click to view

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.

Example - click to view

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

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.

Example - click to view

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

Arrays:

randomItem()

Usage: randomItem(array: Array): any

Returns a random item from an array.
Returns undefined if the array is empty.

Example - click to view

randomItem(["foo", "bar", "baz"]); // "bar"
randomItem([ ]);                   // undefined

randomItemIndex()

Usage: randomItemIndex(array: Array): [item: any, index: number]

Returns a tuple of a random item and its index from an array.
If the array is empty, it will return undefined for both values.

Example - click to view

randomItemIndex(["foo", "bar", "baz"]); // ["bar", 1]
randomItemIndex([ ]);                   // [undefined, undefined]
// using array destructuring:
const [item, index] = randomItemIndex(["foo", "bar", "baz"]);
// or if you only want the index:
const [, index] = randomItemIndex(["foo", "bar", "baz"]);

takeRandomItem()

Usage: takeRandomItem(array: Array): any

Returns a random item from an array and mutates the array by removing the item.
Returns undefined if the array is empty.

Example - click to view

const arr = ["foo", "bar", "baz"];
takeRandomItem(arr); // "bar"
console.log(arr);    // ["foo", "baz"]

randomizeArray()

Usage: randomizeArray(array: Array): Array

Returns a copy of the array with its items in a random order.
If the array is empty, the originally passed array will be returned.

Example - click to view

randomizeArray([1, 2, 3, 4, 5, 6]); // [3, 1, 5, 2, 4, 6]

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README.md

README.md

UserUtils

Table of Contents:

Installation:

Preamble:

License:

Features:

DOM:

onSelector()

initOnSelector()

getSelectorMap()

getUnsafeWindow()

insertAfter()

addParent()

addGlobalStyle()

preloadImages()

openInNewTab()

interceptEvent()

interceptWindowEvent()

amplifyMedia()

Math:

clamp()

mapRange()

randRange()

Misc:

autoPlural()

pauseFor()

debounce()

fetchAdvanced()

Arrays:

randomItem()

randomItemIndex()

takeRandomItem()

randomizeArray()

Files

README.md

Latest commit

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README.md

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UserUtils

Table of Contents:

Installation:

Preamble:

License:

Features:

DOM:

onSelector()

initOnSelector()

getSelectorMap()

getUnsafeWindow()

insertAfter()

addParent()

addGlobalStyle()

preloadImages()

openInNewTab()

interceptEvent()

interceptWindowEvent()

amplifyMedia()

Math:

clamp()

mapRange()

randRange()

Misc:

autoPlural()

pauseFor()

debounce()

fetchAdvanced()

Arrays:

randomItem()

randomItemIndex()

takeRandomItem()

randomizeArray()