Over the last couple of months the V8 team focused on bringing the performance of newly added ES2015 and other even more recent JavaScript features on par with their transpiled ES5 counterparts.
Motivation
Before we go into the details of the various improvements, we should first consider why performance of ES2015+ features matter despite the widespread usage of Babel in modern web development:
- First of all there are new ES2015 features that are only polyfilled on demand, for example the Object.assign builtin. When Babel transpiles object spread properties (which are heavily used by many React and Redux applications), it relies on Object.assign instead of an ES5 equivalent if the VM supports it.
- Polyfilling ES2015 features typically increases code size, which contributes significantly to the current web performance crisis, especially on mobile devices common in emerging markets. So the cost of just delivering, parsing and compiling the code can be fairly high, even before you get to the actual execution cost.
- And last but not least, the client side JavaScript is only one of the environments that relies on the V8 engine. There’s also Node.js for server side applications and tools, where developers don’t need to transpile to ES5 code, but can directly use the features supported by the relevant V8 version in the target Node.js release.
Source: V8 JavaScript Engine: High-performance ES2015 and beyond
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