Javascript Experienced Interview Questions And Answers
javascript experienced interview questions and answers
Javascript experienced interview questions are designed to test the in-depth knowledge and practical experience of a candidate in using the programming language. They cover a wide range of topics such as fundamental concepts, advanced concepts, design patterns, best practices, and troubleshooting techniques. Some common questions focus on data types, function scope, closures, hoisting, event handling, AJAX, DOM manipulation, and debugging. The answers to these questions require a strong understanding of not only the syntax and features of javascript but also its role in web development. Good communication skills and the ability to explain complex concepts in a simple manner are also important in impressing the interviewer.
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1 - What is the difference between “undefined” and “null” in JavaScript?
“Undefined” refers to a variable that has been declared but has not been assigned a value, while “null” refers to a value that represents nothing or empty.
2) What are the different data types in JavaScript?
JavaScript has six primitive data types: string, number, boolean, null, undefined, and symbol. It also has a complex data type called “object.”
3) How do you declare a variable in JavaScript?
Variables can be declared using the “var”, “let”, or “const” keywords. For example: “var num = 10;” or “let name = ‘John’;”
4) What is hoisting in JavaScript?
Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution.
5) What is the use of “this” keyword in JavaScript?
“This” refers to the current object and is used to access or manipulate its properties and methods.
6) Explain the difference between “==” and “===” operators.
“==” checks for equality in value, while “===” checks for equality in value and data type.
7) How do you declare a function in JavaScript?
Functions can be declared with the “function” keyword, followed by the function name, and then the parenthesis containing the function parameters. For example: “function sum(a,b){ return a + b; }”
8) Explain the concept of closures in JavaScript.
A closure is an inner function defined within another function, allowing the inner function to access the outer function's variables and scope even after the outer function has returned.
9) What is a callback function in JavaScript?
A callback function is a function passed as an argument to another function and is executed later when a certain event occurs or when the parent function finishes its execution.
10) How do you create an object in JavaScript?
Objects can be created using the “Object” constructor or using object literal notation. For example: “let person = new Object();” or “let person = {name:'John', age:30};”
11) What is an event in JavaScript?
Events are actions or occurrences that happen in the browser, such as a user clicking on a button or the page finishing loading.
12) What is the difference between “let” and “var”?
“Var” variables are function scoped, while “let” variables are block scoped. This means that “var” variables can be accessed outside the function they were declared in, while “let” variables cannot be accessed outside the block they were declared in.
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13) What is “NaN” in JavaScript?
“NaN” stands for “Not a Number” and is a data type that is returned when a mathematical operation or function expects a number but receives something else.
14) How do you add an element to an array in JavaScript?
Elements can be added to an array using the “push” method or by specifying the index where the element should be inserted. For example: “arr.push('New Element');” or “arr[2] = ‘New Element’;”
15) Explain the difference between “var”, “let”, and “const”.
“Var” variables can be redeclared and reassigned, “let” variables can be reassigned but not redeclared, and “const” variables cannot be reassigned or redeclared.
16) What is the purpose of the “use strict” directive in JavaScript?
“use strict” enables strict mode, which enforces stricter rules and better error handling in JavaScript.
17) Explain the difference between “slice” and “splice” methods.
“Slice” method returns a shallow copy of an array, while “splice” method modifies the original array by removing or replacing elements.
18) What is a promise in JavaScript?
A promise is an object that represents the eventual completion or failure of an asynchronous operation and allows for better handling of asynchronous tasks.
19) How do you debug JavaScript code?
JavaScript code can be debugged using the browser's developer tools, console.log statements, or third party tools such as Chrome DevTools and Firebug.
20) What is the “typeof” operator used for in JavaScript?
The “typeof” operator is used to determine the data type of a variable or expression. For example, “typeof num” would return “number.”
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