How to pass the JS caching test?
The concept of inline caching is based on the empirical observation that the objects that occur at a particular call site are often of the same type. In those cases, performance can be increased greatly by storing the result of a method lookup "inline"; i.e., directly at the call site. To facilitate this process, call sites are assigned different states. Initially, a call site is considered to be "uninitialized". Once the language runtime reaches a particular uninitialized call site, it performs the dynamic lookup, stores the result at the call site and changes its state to "monomorphic". If the language runtime reaches the same call site again, it retrieves the callee from it and invokes it directly without performing any more lookups. To account for the possibility that objects of different types may occur at the same call site, the language runtime also has to insert guard conditions into the code. Most commonly, these are inserted into the preamble of the callee rather than at the call site to better exploit branch prediction and to save space due to one copy in the preamble versus multiple copies at each call site. If a call site that is in the "monomorphic" state encounters a type other than the one it expects, it has to change back to the "uninitialized" state and perform a full dynamic lookup again.
FAQs on JavaScript Caching
JavaScript caching allows browsers to store JS files locally so they don’t need to be downloaded again on repeat visits, reducing load time and improving performance.
Caching reduces network requests, lowers page load times, and improves overall user experience—especially for returning visitors.
Caching itself is not a direct ranking factor, but faster load times and better performance metrics can positively support SEO.
Browsers use HTTP cache headers like Cache-Control, Expires, and ETag to determine how long JavaScript files should be stored and when they should be revalidated.
For static JavaScript files, long cache durations (for example, 6 months or 1 year) are recommended. Versioned filenames should be used to ensure updates are picked up correctly.
Cache busting is a technique where a file’s name or query string changes (for example, app.123.js) when the file is updated, forcing browsers to download the latest version.
Yes, if cache headers are misconfigured. Without proper cache busting, users may continue to see old JavaScript files after updates.
Yes. CDNs cache JavaScript files at edge locations, improving load times globally and reducing server load. Cache rules should be configured carefully.
Browser caching stores files on the user’s device, while CDN caching stores files on distributed servers closer to users. Both work together to improve performance.
Use browser DevTools (Network tab) to inspect cache headers and response details, or run performance tools to confirm whether repeat visits reuse cached JavaScript files.