A big difference between ES5 and ES6&#x2F;7 is that the former passes through our old, highly-tuned optimizing engine Crankshaft [0] and the latter passes through our new optimizing engine TurboFan [1]. The team&#x27;s expertise optimizing Crankshaft can certainly be leveraged in TurboFan, but it&#x27;s not an apples-to-apples comparison. In the future, TurboFan will handle ES5 code as well.<p>tl;dr we&#x27;re changing engines mid-flight and that has as much to do with performance differences as the ES6 features themselves.<p>[0]: <a href="http:&#x2F;&#x2F;blog.chromium.org&#x2F;2010&#x2F;12&#x2F;new-crankshaft-for-v8.html" rel="nofollow">http:&#x2F;&#x2F;blog.chromium.org&#x2F;2010&#x2F;12&#x2F;new-crankshaft-for-v8.html</a>
[1]: <a href="http:&#x2F;&#x2F;v8project.blogspot.com&#x2F;2015&#x2F;07&#x2F;digging-into-turbofan-jit.html" rel="nofollow">http:&#x2F;&#x2F;v8project.blogspot.com&#x2F;2015&#x2F;07&#x2F;digging-into-turbofan-...</a>