CollectionsField terms148
Core jargon for software architecture, delivery, and engineering culture.
For developers early in their career, and anyone who works closely with them.
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A defined set of endpoints and rules that lets one piece of software request data or functionality from another, without needing to know how it's implemented internally.
Example:Calling GET /users/42 to fetch a user's profile without knowing what database sits behind it.
Existing clients keep working without modification after something behind the scenes has changed.
Example:A new API version adds an optional 'nickname' field, but old clients that never send it keep working unmodified.
A change to an API or system's behavior that forces existing consumers to update their own code, or their integration stops working.
Example:Renaming a required field in an API response.
The agreed-upon set of inputs, outputs, and behavior that two systems promise to honor when communicating.
Example:A weather API promising to always return temperature in Celsius.
Taking raw transferred data — JSON, bytes — and turning it back into a usable object your code can work with.
A query language for APIs where the client specifies exactly what data it needs, and the server returns exactly that — nothing more, nothing less.
Example:A mobile client fetches only `user.name` and `user.avatar` instead of the full user object a REST endpoint would return.
An operation that produces the same end result no matter how many times it's performed, so retrying it is always safe.
Example:A payment API where retrying a failed request with the same idempotency key charges the customer only once.
A function that runs in between an incoming request and the final handler, used to add cross-cutting behavior like logging, auth checks, or parsing.
Example:An Express middleware that checks for a valid auth token on every request before it reaches the route handler.
Breaking a large result set into pages of a fixed size, so callers fetch one chunk at a time instead of the entire collection.
A piece of code that implements a browser API or language feature in environments where it doesn't natively exist yet.
Example:A script that adds `Array.prototype.flat` to older browsers that don't support it.
Capping how many requests a client can make to an API in a given time window, to protect the server from overload and abuse.
Example:An API that returns 429 Too Many Requests after 100 calls per minute from a single token.
An architectural style for HTTP APIs where resources are addressed by URLs and manipulated with standard HTTP methods (GET, POST, PUT, DELETE).
A versioning convention where version numbers follow `major.minor.patch` — patch for bug fixes, minor for backward-compatible additions, major for breaking changes.
Converting an object into a flat, transferable format — like JSON or bytes — so it can be sent over a network or saved to disk.
The server remembers information from earlier interactions and uses it to affect how it handles later requests.
Example:A shopping cart that remembers what you added.
The server keeps no memory of past requests — each request carries all the information needed to handle it on its own.
Example:Ordering at a fast-food counter where every visit stands alone.
A callback pattern where one service notifies another by sending an HTTP POST to a URL the receiver registered in advance — triggered by an event, not a poll.
Example:Stripe POSTing to your `/webhook` endpoint when a payment succeeds, instead of you polling Stripe every second.
A persistent two-way connection between client and server over a single TCP connection — either side can push data to the other at any time without a request.
Example:A live chat app or a collaborative editor where updates appear in real time without polling.
Hiding how something works internally and exposing only the interface a caller needs to use it.
Example:Calling sendEmail() without knowing about the servers and formatting happening underneath.
How tightly a module's responsibilities relate to one single purpose, rather than being a grab-bag of unrelated tasks.
Example:A module that only sends emails is more cohesive than one that also handles payments and analytics.
A way of describing how an algorithm's run time or memory use grows as its input size grows, ignoring constant factors.
Example:Saying a linear search is O(n) because checking twice as many items takes roughly twice as long, versus O(1) for a hash lookup that takes the same time regardless of size.
The single slowest component in a system that caps overall speed, no matter how fast every other part runs.
Example:A checkout flow that's fast everywhere except one synchronous call to a slow tax API, which caps the whole flow's speed.
Standard, repetitive code that must be written in nearly the same form every time, carrying little logic of its own.
Example:The near-identical setup code you write every time you start a new file.
A structured process where one or more teammates read proposed changes before they merge, checking for bugs, design problems, and maintainability issues.
A surface-level pattern in code — not a bug by itself — that often signals a deeper design problem worth investigating.
Example:
The packaged output of a build — a compiled binary, container image, or bundle — that gets promoted through environments and ultimately deployed.
Example:The packaged, ready-to-deploy app bundle produced by a build.
Running two identical production environments and instantly switching all traffic from the old one to the new one, enabling near-zero-downtime releases and instant rollback.
Example:Flipping traffic from the old live environment to the new standby one instantly.
A function that captures and 'remembers' variables from the scope it was defined in, even after that scope has finished executing.
Example:A counter factory that returns a function with its own private count variable — each call to the factory produces a counter that doesn't share state with others.
Same input, same output — every single time, with no variation between runs.
Example:A sorting function that returns the exact same order every time you give it the exact same list.
The system keeps responding to requests even when part of it has failed — one of the three properties in the CAP theorem.
Example:An e-commerce site that keeps taking orders even though its recommendation engine is down.
A network of geographically distributed servers that cache and serve static assets from wherever is closest to the user.
Example:A user in Tokyo fetching your CSS from a CDN node in Tokyo instead of your origin server in Virginia.
A scenario where multiple edge cases occur at once, making it far rarer and harder to anticipate than any single edge case alone.
Example:The last item in stock, bought at midnight, during a sale, with an expired coupon.
A rare but technically valid input or condition that sits at the boundary of what the system was designed to handle.
Example:A name with an apostrophe, like 'O'Brien'.
A test that drives the full application as a user would — through the UI, through the backend, against a real or near-real environment.
How much of the system — and how many users — would be affected if a given change or component fails.
Example:A bug in shared login has a bigger blast radius than a bug in a rarely-used settings page.
A built-in constraint that prevents a system or user from taking an action known to be incorrect or unsafe.
Example:A form that won't accept a negative price.
Releasing a change to a small slice of users first and progressively widening it, rather than shipping to everyone at once.
The process of verifying that someone is who they claim to be.
Example:Logging in with a password or a magic link.
Deciding what an already-authenticated user is allowed to do or see.
Example:An admin can delete records; a regular user can only view them.
An attack that tricks a logged-in user's browser into making an unwanted request to your app — exploiting the fact that browsers automatically attach cookies to requests.
A named pointer to a line of commits in a repository, letting work proceed in parallel without touching the main codebase.
Example:Creating a `feature/login-redesign` branch to develop a feature without disrupting what's already deployed.
A saved snapshot of changes to a repository, along with a message describing what changed and why.
When two branches have made incompatible changes to the same part of the same file, requiring a human to decide what the final version should be.
A data structure the database maintains alongside a table to speed up queries on specific columns, at the cost of slower writes and more storage.
A versioned, usually irreversible script that changes a database's schema or data — adding a column, renaming a table, backfilling values.
Structuring a relational database to eliminate redundancy by storing each fact in exactly one place and referencing it by key everywhere else.
Building behavior by assembling small, independent objects instead of extending a shared base class, avoiding deep and fragile class hierarchies.
Example:A game character built by combining a Movable, a Damageable, and a Renderable component instead of extending one monolithic Character base class.
Storing the result of expensive work so a later request can reuse it instead of recomputing or refetching from scratch.
Example:Storing a product page's rendered HTML for 60 seconds so the next 1,000 visitors get it instantly instead of hitting the database.
A tool that takes source modules (JavaScript, CSS, assets) with their dependency graphs and outputs one or more optimized files for the browser.
Example:Webpack, Vite, Rollup — they resolve imports, apply transforms, and produce the production build.
New functionality can be added without rewriting or breaking the code that already works.
Example:A payment system that supports a new provider by implementing one interface, without touching existing checkout code.
A pattern that detects when a downstream service is failing and stops sending it requests temporarily, instead of letting every caller time out and pile up.
Example:After five consecutive failures to a payment API, the circuit 'opens' and immediately returns an error for the next 30 seconds rather than letting callers wait.
Example:A Playwright script that logs in, adds an item to a cart, and checks the order confirmation page.
Example:Releasing a change to 5% of users, watching the metrics, then expanding.
Example:An image tag on a malicious site that fires a DELETE request to your bank's API using the user's active session.
Combining the changes from one branch into another, producing a unified history that includes both lines of work.
A library that maps database tables to code objects, letting you query and manipulate data using the language's own constructs instead of writing raw SQL.
Example:Prisma, Hibernate, ActiveRecord — write `User.findMany({ where: { active: true } })` instead of a SELECT statement.