Immer is a popular library for managing immutable state in JavaScript applications. While it primarily focuses on ensuring immutability, Immer also provides features for handling validation and schema enforcement.

In this article, we will explore how we can leverage Immer to validate and enforce schemas in our application state.

Why Validate and Enforce Schemas?

Having a well-defined schema for your application state is crucial for maintaining data integrity and consistency. By validating and enforcing schemas, we can ensure that our state remains in the desired format and meets our application requirements.

Setting up Immer

Before we dive into schema validation, let’s quickly set up Immer in our project. You can install Immer using npm or yarn:

npm install immer

yarn add immer

Once installed, you can import it into your code:

import produce from 'immer';

Schema Validation with Immer

Immer provides the currentState and patches arguments to the producer function, allowing us to access and validate the current state.

Let’s say we have a simple schema that requires a name field in our application state. We can enforce this schema using Immer’s produce function as follows:

const validateSchema = (currentState) => {
  if (!currentState.name) {
    throw new Error('Invalid schema: name is missing.');
  }
};

const newState = produce(currentState, (draftState) => {
  validateSchema(draftState);
});

In the above code, we define a validateSchema function that checks if the name field exists in the currentState. If the field is missing, an error is thrown.

Using the produce function, we pass the current state and a callback that gets executed with a draft state. Inside the callback, we can then validate the draft state using our validateSchema function.

By throwing an error, we prevent any modifications to the state that don’t adhere to the schema.

Avoiding Invalid State Modifications

In addition to schema validation, Immer provides a way to prevent modifications to the state that violate the schema by using the patches argument.

const enforceSchema = (currentState, patches) => {
  patches.forEach((patch) => {
    if (patch.path === 'name' && !currentState.name) {
      throw new Error('Invalid modification: name field cannot be added.');
    }
  });
};

const newState = produce(currentState, (draftState, patches) => {
  validateSchema(draftState);
  enforceSchema(draftState, patches);
});

In the above code, we define an enforceSchema function that validates any modifications performed on the state. By iterating over the patches, we can check if the modification is trying to add the name field when it doesn’t exist in the original state.

If the modification violates the schema, we throw an error, preventing the invalid change from being applied to the state.

Conclusion

By utilizing Immer’s produce function along with custom validation and enforcement logic, we can handle schema validation and enforcement effectively. This ensures that our application state remains consistent and adheres to the desired schema.

Remember to leverage Immer’s capabilities alongside other validation libraries or techniques to build robust and reliable state management in JavaScript applications.

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