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Discussion on: You either make 'var', 'let' or keep 'const' in JavaScript

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peerreynders

ES2015 (ES6) actually.

But I imagine that the whole primitive values are immutable thing was established much, much earlier—leading to a situation where creating a "constant binding" was easy and relatively cheap in terms of run-time performance.

Facilities for creating immutable objects exist (Object.freeze() which is only shallow) but come with run-time overhead.