Caching is one of the most effective ways to improve application performance.

It can also produce some of the strangest bugs developers encounter.

Why Cache?

Suppose a page repeatedly requests the same expensive data.

Without caching:

Request ↓ Application ↓ Database ↓ Response

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With caching:

Request ↓ Cache ↓ Response

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The expensive operation can potentially be avoided.

Cache-Aside Pattern

One common strategy is:

let value = await cache . get ( key );

if ( ! value ) { value = await database . getData (); await cache .…