Backend Developer 路 Intern to senior
Backend interviews test how you store, process and serve data reliably: language fundamentals, SQL and indexing, concurrency, API design and how systems behave under load.
131 questions
Unit tests check one small piece of code in isolation, integration tests check that several pieces work together (for example code plus a real database), and end-to-end tests drive the whole application the way a user would.
Normalise the string (lower case, remove non-alphanumeric characters), then compare characters from both ends moving inward with two pointers. This is O(n) time and O(1) extra space beyond the normalised copy.
Give a 60-90 second summary in three parts: what you do now, one or two achievements that show your strengths, and why this role is the logical next step.
Connect two or three of your strongest, provable skills directly to the needs in the job description, give a short piece of evidence for each, and show genuine interest in the team鈥檚 work.
Give specific evidence of deliberate learning through projects, feedback, reading, experimentation or mentoring rather than listing technologies.
Connect something specific about the company, product, engineering challenges or team to your own experience and career goals.
require is the CommonJS module system, which loads modules synchronously at runtime, while import is the ES module standard, which is statically analysed, asynchronous and supports top-level await and tree shaking.
Middleware are functions that receive the request, response and a next callback; they run in the order they are registered and can modify the request, end the response or pass control on with next().
UNION combines two result sets and removes duplicate rows, while UNION ALL combines them and keeps every row, which makes it faster.
A const is a compile-time constant that must be assigned where it is declared, while a readonly field can be assigned at declaration or in the constructor, so its value can be decided at runtime.
Both pass an argument by reference, but ref requires the variable to be initialised before the call, while out requires the method to assign a value before it returns.
*args collects extra positional arguments into a tuple and **kwargs collects extra keyword arguments into a dictionary, which lets a function accept a variable number of arguments.
Vertical scaling means giving one machine more CPU, memory or disk, while horizontal scaling means adding more machines and spreading the load across them.
Volumes are storage managed by Docker that lives outside a container鈥檚 writable layer, so data such as database files survives when the container is removed or replaced.
The test pyramid is a guideline to have many fast unit tests at the base, fewer integration tests in the middle and only a small number of slow end-to-end tests at the top, so the suite stays fast and reliable.
Walk through the array once while storing each number鈥檚 index in a hash map; for every number, check whether target minus that number is already in the map. This runs in O(n) time and O(n) space.
any turns off checking. unknown is a type-safe any: you must narrow it before use. never means a value cannot exist, used for exhaustive checks and functions that always throw.
Generics are type parameters: they let a function, class or type work with many types while keeping the relationship between inputs and outputs, instead of falling back to any.
A union (A | B) is a value that is one of the members. An intersection (A & B) is a value that must satisfy both types at once.
Utility types are built-in helpers that transform an existing type: Partial makes every field optional, Required the opposite, Pick keeps a set of keys, Omit removes them, and Record builds a key/value map.