These are libraries for use in userscripts by developers.
Using waitForElement.js as an example – replace the filename in instructions with the library you would like to use.
Add a @require entry to metadata of the userscript:
// @require https://.com/rybak/userscript-libs/raw/<commit>/waitForElement.js
Replace the <commit> placeholder with the hash of the commit that you want to use.
If you want to publish the userscript on Greasy Fork, you'll have to follow their policy on external scripts. This can be done using the JSDelivr CDN or other content delivery networks approved by Greasy Fork. Greasy Fork (rightly) doesn't allow using a branch or a tag.
// @require https://cdn.jsdelivr.net/gh/rybak/userscript-libs@<commit>/waitForElement.js
Provides a way for userscripts to wait for native HTML or SVG elements to be loaded, before performing some operation on them. Function waitForElement takes a selector as a parameter and returns a Promise. The returned Promise gets resolved with an Element corresponding to the given selector, when the element appears in the document. Usage:
waitForElement('#targetId').then(target => {
// extract information from `target`:
const text = target.innerText;
// add your own elements to `target`:
target.append("Hello, world!");
});