WKWebView lots of input lag with contenteditable elements and emoji

Originator:JoshyHargreaves
Number:rdar://32845692 Date Originated:June 19 2017
Status:Open Resolved:
Product:iOS + SDK Product Version:
Classification:Bug Reproducible:Always
 
When editing a contenteditable HTML element in WKWebView with a moderate amount of content, adding emoji symbols from the keyboard causes a lot of input lag and the whole UI thread starts to lock up and input lags becomes very intense rendering the input useless. The input lags seems to increase with the size of the content of the contenteditable element.

Video of bug in question: https://twitter.com/joshyhargreaves/status/875821102567706624
Github repo with sample project: https://github.com/joshyhargreaves/wkwebview-slow-emoji

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