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
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It catches type errors in the editor and at build time, and it documents the shape of data for the next person who reads the code.
Both describe object shapes. interface can be merged and is preferred for public object contracts; type can express unions, intersections and primitives, and cannot be reopened later.
Node.js is a JavaScript runtime built on Chrome's V8 engine that runs your JavaScript on a single main thread and uses non-blocking I/O, so one thread can handle many concurrent connections.
package.json lists your project's dependencies with allowed version ranges, while package-lock.json records the exact versions that were installed so every machine gets an identical dependency tree.
INNER JOIN returns only rows that have a match in both tables, while LEFT JOIN returns every row from the left table and fills the right table's columns with NULL when there is no match.
WHERE filters individual rows before grouping, while HAVING filters groups after GROUP BY, so only HAVING can use aggregate functions like COUNT or SUM.
DELETE removes selected rows and can be rolled back, TRUNCATE quickly removes all rows and keeps the table structure, and DROP removes the entire table including its structure.
A primary key uniquely identifies each row in its own table and cannot be NULL, while a foreign key is a column that references the primary key of another table to link the two.
A value type variable holds its data directly and is copied on assignment, while a reference type variable holds a reference to an object, so assignment copies the reference and both variables see the same object.
A string is immutable, so every change creates a new string object, while StringBuilder is a mutable buffer that modifies its contents in place, making it much faster for repeated concatenation.
The JVM runs Java bytecode, the JRE is the JVM plus the standard libraries needed to run Java programs, and the JDK is the JRE plus the development tools such as the compiler (javac).
== compares primitives by value and objects by reference (whether they are the exact same object), while equals() compares the logical content of two objects when the class overrides it.
String is immutable, StringBuilder is a mutable and fast but not thread-safe buffer, and StringBuffer is a mutable buffer with synchronized methods that is thread-safe but slower.
final is a keyword that prevents reassigning a variable, overriding a method or extending a class; finally is a block that always runs after try/catch for cleanup; finalize() was a method called by the garbage collector and is now deprecated.
A list is mutable and can be changed after creation, while a tuple is immutable; tuples are slightly faster, use less memory and can be used as dictionary keys when their items are hashable.
== checks whether two objects have equal values, while is checks whether they are the exact same object in memory.
Git is a distributed version control system that tracks changes to files on your machine; GitHub is a hosting service for Git repositories that adds collaboration features such as pull requests, code review and CI.
git fetch downloads new commits from the remote without changing your working branch; git pull runs a fetch and then merges (or rebases) those commits into your current branch.
A virtual machine runs a full guest operating system on virtualised hardware, while a container shares the host鈥檚 kernel and isolates only the process, its filesystem and resources, which makes containers much lighter and faster to start.
An image is a read-only template made of layers that contains the application and its dependencies; a container is a running (or stopped) instance of an image with its own writable layer on top.