Handling API Versioning and Backward Compatibility on the Frontend

When integrating with APIs, versioning and backward compatibility are critical to ensure a smooth user experience and prevent breaking changes. Here’s how I handle it:

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1️⃣ API Versioning Strategies

A. URL-Based Versioning (Recommended)

• The API endpoint includes the version number (e.g., /api/v1/users).
• The frontend can switch between versions based on feature requirements.
• Example:

  const API_BASE_URL = "https://example.com/api/v1";
  fetch(`${API_BASE_URL}/users`);

B. Header-Based Versioning

• The API version is passed in request headers.
• Example:

  fetch("/api/users", {
    headers: {
      "Accept-Version": "v1",
    },
  });

C. Query Parameter Versioning

• The version is passed as a query string.
• Example:

  fetch("/api/users?version=1");

D. GraphQL Versioning

• Instead of multiple API versions, we deprecate fields gracefully and introduce new fields.
• Example:

  type User {
    id: ID!
    name: String!
    email: String @deprecated(reason: "Use primaryEmail instead")
    primaryEmail: String
  }

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2️⃣ Ensuring Backward Compatibility

To avoid breaking older frontend versions when the API changes, I follow these best practices:

A. Feature Detection (Graceful Degradation)

• Check if the new API feature exists before using it.
• Example:

  fetch("/api/v1/users")
    .then((res) => res.json())
    .then((data) => {
      if (data.newField) {
        console.log("Using new API feature");
      } else {
        console.log("Fallback to older version");
      }
    });

B. Maintain Compatibility Layers (Adapters)

• Create a helper function that adapts API responses to match expected data structures.
• Example:

  function normalizeUserResponse(data: any) {
    return {
      id: data.id,
      name: data.fullName || data.name, // Handle old and new versions
      email: data.email || data.primaryEmail,
    };
  }

  fetch("/api/v1/users")
    .then((res) => res.json())
    .then((data) => console.log(normalizeUserResponse(data)));

C. Feature Flagging for API Changes

• Enable new API versions gradually using feature flags.
• Example using LaunchDarkly:

  if (featureFlags.isEnabled("new-api-endpoint")) {
    fetch("/api/v2/users");
  } else {
    fetch("/api/v1/users");
  }

D. API Version Fallback Mechanism

• If the latest API version is unavailable, fallback to a stable version.
• Example:

  async function fetchUserData() {
    try {
      let response = await fetch("/api/v2/users");
      if (!response.ok) throw new Error("V2 not available");
      return await response.json();
    } catch (error) {
      return await fetch("/api/v1/users").then((res) => res.json());
    }
  }

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3️⃣ Monitoring and Handling API Deprecations

• Log API usage to detect old versions still in use.
• Set deprecation warnings in API responses.
• Example:

  {
    "data": { "id": 1, "name": "John Doe" },
    "warning": "This API version (v1) is deprecated and will be removed on MM/DD/YYYY."
  }

• Notify users before an API is retired.

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✅ Summary: Best Practices

✔ Use URL-based API versioning (e.g., /api/v1/)

✔ Implement adapters to handle different API structures

✔ Detect new API features before using them (feature detection)

✔ Gradually migrate using feature flags

✔ Implement fallback mechanisms for missing APIs

✔ Monitor and log API usage to phase out old versions