Javascript Programming Interview Questions And Answers
a Complete Guide to
Javascript Programming Interview Questions and Answers are a set of commonly asked questions that test the knowledge and skills of a candidate in Javascript programming. These questions aim to assess the candidate's understanding of the core language concepts, data types, operators, control structures, functions, and other important topics. The answers to these questions showcase the candidate's problem-solving approach, ability to write efficient and effective code, and proficiency in using Javascript to build dynamic web applications. It is essential for any candidate preparing for a Javascript programming job to have a good understanding of these interview questions and be able to provide clear and concise answers to stand out in the highly competitive job market.
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1 - What is the difference between ‘undefined’ and ‘null’ in Javascript?
Undefined means a variable has been declared but has not been assigned a value. Null represents an intentional absence of a value.
2) Explain the difference between ‘==’ and ‘===’ in Javascript.
‘==’ compares only the values of the two operands, while ‘===’ compares both the value and the type of the operands.
3) What is a closure in Javascript?
A closure is a combination of a function and the lexical environment within which that function was declared. This allows the function to access variables in its outer scope even after the outer function has returned.
4) What is the purpose of the ‘this’ keyword in Javascript?
The ‘this’ keyword refers to the current execution scope of a function. Its value will depend on how a function is invoked.
5) What is the difference between ‘var’, ‘let’ and ‘const’ keywords in Javascript?
‘var’ is function scoped, ‘let’ is block scoped, and ‘const’ is block scoped like ‘let’, but its value can never be reassigned.
6) How do you handle errors in Javascript?
Errors can be handled using ‘try catch’ blocks or by using ‘throw’ to create custom errors.
7) What is hoisting in Javascript?
Hoisting is the process by which variable and function declarations are moved to the top of their respective scopes during compilation.
8) What is a pure function in Javascript?
A pure function is a function that always returns the same output for a given input, and it does not modify any external state.
9) How can you check if a variable is an array in Javascript?
The ‘Array.isArray()’ method can be used to check if a variable is an array.
10) What is the difference between synchronous and asynchronous code execution?
Synchronous code is executed in a single thread, one statement at a time, while asynchronous code allows other operations to run while the code is being executed.
11) What is the event loop in Javascript?
The event loop is responsible for handling asynchronous code execution in Javascript. It continuously checks the message queue for new events and executes them in the call stack.
12) Explain the difference between ‘splice’ and ‘slice’ in Javascript.
‘splice’ is used to add or remove elements from an array in place, while ‘slice’ returns a new array containing the selected elements.
13) How can you opt out of Javascript's automatic type conversions?
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By using the strict equality operator, ‘===’.
14) What is a higher order function in Javascript?
A higher order function is a function that either takes a function as an argument or returns a function as its result.
15) How can you optimize performance in Javascript?
Performance in Javascript can be optimized by minimizing DOM manipulation, using event delegation, avoiding excessive global variables, and using caching and lazy loading techniques.
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