JavaScript
Modern JavaScript patterns - from first principles to production-grade code.
Curriculum preview
- 02Values
- 16Array Transforms
- 22Promises and async/await
- 28DOM Manipulation
+ 39 more lessons
Explore JavaScript
Software engineer
159 practical lessons across 3 courses
In 45 minutes, one outdated order-routing server turned a reused feature flag into millions of unintended trades. The incident shows why deployment correctness and risk controls must be designed together.
A stored birthday can display as the previous day because JavaScript `Date` converts a calendar date into a timestamp. Temporal provides separate types for calendar dates, exact timestamps, and scheduled events.
A dirty read returns an uncommitted value from another transaction. If that transaction rolls back, the reader observed a value that was never part of committed database state.
A transaction reads the same row twice and gets two different committed values. The isolation level determines whether both reads use the same database state.
A transaction repeats a search and finds an additional matching row. The existing rows did not change, but another transaction committed a new row that satisfies the same query.
RFC 10008 gives HTTP a method for safe queries with a body. It fills the awkward gap between long GET URLs and POST requests that normally reserved for mutations.
Deploying code to production is irreversible in the short term - when something goes wrong, rolling back requires another deploy, which takes time and may have its own risks. Feature flag allows you to revert fast
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