Senior Developer 路 5+ years
Senior interviews are less about the right answer and more about how you decide. Expect open-ended questions where you must state assumptions, compare options, name the costs of each and explain what you would measure.
78 questions
Keep the answer professional and future-focused: explain what you are looking for next without attacking your current or former employer.
The event loop is the mechanism that lets single-threaded JavaScript handle asynchronous work: it runs the call stack to empty, then runs all queued microtasks (promises), then takes the next task (timers, events) from the queue.
In JavaScript every object has an internal link to another object called its prototype, and property lookups walk up this prototype chain until the property is found or the chain ends.
Debounce waits until the user stops triggering an event for a set time before running the function; throttle runs the function at most once per time interval no matter how often the event fires.
useMemo caches the result of a calculation, while useCallback caches a function definition; both only recompute when their dependencies change.
Updating state triggers a re-render, while changing a ref's .current value does not; use state for data shown on screen and refs for DOM access or values that must persist without causing renders.
CSR renders in the browser after JavaScript loads, SSR renders the HTML on the server for each request, and SSG renders the HTML once at build time; SSR and SSG give crawlers and users content faster, which helps SEO.
Both download the script without blocking HTML parsing. defer waits until parsing finishes and runs scripts in document order; async runs a script as soon as it is downloaded, which can be before or after parsing and in any order.
The browser parses HTML into a DOM and CSS into a CSSOM, combines them into a render tree, computes layout (reflow), paints pixels and composites layers onto the screen.
Narrowing is when TypeScript shrinks a wide type (such as a union) to a more specific type after a runtime check like typeof, instanceof, in, or a custom type guard.
A string union such as "admin" | "user" exists only in the type system and erases to plain strings. A TypeScript enum compiles to a JavaScript object (unless it is a const enum), which is extra runtime code and a weaker default.
TypeScript fills in types you omit: literals get their literal or widened type, function return types are inferred from return statements, and generic arguments are inferred from the values you pass.
process.nextTick runs its callback right after the current operation, before the event loop continues; setTimeout runs in the timers phase after a minimum delay; and setImmediate runs in the check phase right after the poll (I/O) phase.
Streams process data piece by piece as it arrives instead of loading it all into memory, which lets you handle large files and network data efficiently; they come in Readable, Writable, Duplex and Transform types.
Session authentication stores the login state on the server and gives the browser a session ID cookie, while JWT authentication gives the client a signed token that contains the user's claims so the server can verify it without storing state.
ACID stands for Atomicity, Consistency, Isolation and Durability: a transaction either fully succeeds or fully fails, keeps the data valid, does not interfere with other transactions, and survives crashes once committed.
An index is a separate sorted data structure (usually a B-tree) that lets the database find rows without scanning the whole table, at the cost of extra storage and slower writes.
A clustered index defines the physical order in which the table's rows are stored, so there can be only one per table, while a non-clustered index is a separate structure that points back to the rows.
IEnumerable runs the query in memory using delegates, while IQueryable builds an expression tree that a provider such as Entity Framework translates into SQL, so filtering happens in the database.
Transient services are created every time they are requested, scoped services are created once per HTTP request, and singleton services are created once and shared for the life of the application.