Why Ext.webKitVersion = 0 on Safari 10.11.1 and Google Chrome 59 and Firefox 54.0?

I am using Ext JS 6.5 . I am reading: http://docs.sencha.com/extjs/6.5.0/modern/Ext.html#property-webKitVersion

When I use script

console.log(Ext.isWebKit);

Result on Google Chrome, Safari is true. Result on Firefox is false.

I use script

console.log(Ext.webKitVersion);

The result is 0. Is it means Safari, Chrome, Firefox doesn’t use WebKit?

Question: Why Ext.webKitVersion = 0 on Safari 10.11.1 and Google Chrome 59 and Firefox 54.0? Is it a bug?


Source: stackoverflow-javascript