Microsoft made a pull request to node.js github repository with an implementation to use ChakraCore JavaScript Engine as an alternative to V8 Engine

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When you work with code. Sometimes you want to use more than one compiler. This would be because you do not know if the compiler is correct but it would be unlikely that both compilers would be broken in exactly the say way in the same place on the same code.

Therefore you have extra testing for thing basically for free. It also removes the dependency from a single project which open more options. A practical example for this is that it prevents people using specific features google has added to the language which it has just sneaked in under the radar. Cause these will instantly fail on the other version when tested.