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Apr 2019
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With the increasing complexity of single-page JavaScript applications, managing state predictably is becoming more and more important. Immutability can help to ensure our applications behave consistently, but unfortunately JavaScript doesn't natively support the ability to create immutable objects. Libraries such as Immutable.js filled that gap but introduced new problems because now two kinds of objects and arrays existed in the application, the library's version and the native JavaScript ones. Immer — German for always — is a tiny package that lets you work with immutable state in a more convenient way. It's based on the copy-on-write mechanism, has a minimal API and operates on normal JavaScript objects and arrays. This means that data access is seamless and no large refactoring efforts are needed when introducing immutability to an existing codebase.