JavaScriptEasy
What is the difference between var, let and const in JavaScript?
var is function-scoped and can be redeclared; let and const are block-scoped, and const cannot be reassigned after it is set.
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What is hoisting in JavaScript?
Hoisting is JavaScript moving declarations to the top of their scope during compilation, so functions and var variables can be referenced before the line where they are written.
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What is the difference between map, filter and reduce in JavaScript?
map transforms every item into a new array of the same length, filter keeps only items that pass a test, and reduce folds the whole array into a single value.
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What is the difference between ref and out parameters in C#?
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.
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What are *args and **kwargs in Python?
*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.
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What is a closure in JavaScript and why is it useful?
A closure is a function that keeps access to the variables of the scope where it was created, even after that outer function has finished running.
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How does the this keyword work in JavaScript?
this is decided by how a function is called, not where it is written: as a method it is the object before the dot, with new it is the new object, and arrow functions inherit it from the enclosing scope.
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What is LINQ in C# and what is deferred execution?
LINQ (Language Integrated Query) lets you query collections, databases and XML with a consistent syntax, and deferred execution means a query does not run when you define it but when you enumerate the results.
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What are the main features of Java 8: lambdas, streams and Optional?
Java 8 introduced lambda expressions, functional interfaces, the Stream API for declarative collection processing, Optional to represent missing values, default methods in interfaces, method references and the java.time date and time API.
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Why should you not use a mutable default argument in Python?
Default argument values are evaluated once when the function is defined, so a default list or dictionary is shared between every call that does not pass its own, causing data to leak between calls.
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How do you flatten a nested array in JavaScript without using flat()?
Recursively walk the array: when an element is an array, flatten it and append the result; otherwise append the element. An iterative version uses an explicit stack to avoid recursion limits.
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What are decorators in Python and how do they work?
A decorator is a function that takes another function and returns a modified version of it, letting you add behaviour such as logging, caching or access control without changing the original code.
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What are generators and the yield keyword in Python?
A generator is a function that uses yield to produce values one at a time and remembers its state between calls, so it can process large or infinite sequences without holding everything in memory.
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