the diff package on npm now includes its own TypeScript type definitions. Users who previously used the @types/diff npm package from DefinitelyTyped should remove that dependency when upgrading JsDiff to v8.

Note that the transition from the DefinitelyTyped types to JsDiff's own type definitions includes multiple fixes and also removes many exported types previously used for options arguments to diffing and patch-generation functions. (There are now different exported options types for abortable calls - ones with a timeout or maxEditLength that may give a result of undefined - and non-abortable calls.) See the TypeScript section of the README for some usage tips.

The Diff object is now a class. Custom extensions of Diff, as described in the "Defining custom diffing behaviors" section of the README, can therefore now be done by writing a class CustomDiff extends Diff and overriding methods, instead of the old way based on prototype inheritance. (I think code that did things the old way should still work, though!)

diff/lib/index.es6.js and diff/lib/index.mjs no longer exist, and the ESM version of the library is no longer bundled into a single file.

The ignoreWhitespace option for diffWords is no longer included in the type declarations. The effect of passing ignoreWhitespace: true has always been to make diffWords just call diffWordsWithSpace instead, which was confusing, because that behaviour doesn't seem properly described as "ignoring" whitespace at all. The property remains available to non-TypeScript applications for the sake of backwards compatibility, but TypeScript applications will now see a type error if they try to pass ignoreWhitespace: true to diffWords and should change their code to call diffWordsWithSpace instead.

JsDiff no longer purports to support ES3 environments. (I'm pretty sure it never truly did, despite claiming to in its README, since even the 1.0.0 release used Array.map which was added in ES5.)