javascript tricky questions

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Tricky Javascript Code Snippets Questions Asked in the Interview (es6/es7/es8/es9)

Prepare for your next 2025 Javascript Coding Interview Questions with these tricky code snippets. Covering ES6/ES7/ES8/ES9 syntax and features, this article provides examples and explanations to help you ace your interview.

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7 Simple but Tricky JavaScript Interview Questions

Do people really ask questions like this? These are all weird esoteric JS things that happen when you write stuff in weird ways. More on reddit.com

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October 16, 2019

JavaScript Tricky Interview Questions 2023

When i was younger, I always wanted to interview people, and I thought to myself 'Ill find the best candidates " "I'll expose the frauds with some special whiteboard question".

When I finally was asked to do so, it was so soo different than what i thought it was going to be like. First of all, it's really hard to get a qualified person in front of you, especially post code bootcamp boom.

Then, you actually empathize with these people being put on the spot and freezing up, on some basic stuff which in the back of your mind you know they know.

I went from trying to catch people being bad, to now helping people get through an interview if the need presents itself. Watching someone crash and burn in an interview is extremely painful.

An interview to me now, is to gauge if they are being truthful about their background and knowledge, and establish if they are junior, intermediate or senior.

I actually give some incredibly easy white boarding questions for a front end dev, but I leave implementation very ambiguous.

Within code sandbox, and you can google anything you want, use the most modern implementations for the following questions :

Show me a usecase and example of array.map, array.filter, array.reduce
Reproduce this 3 column layout with a header and footer, handle it's responsiveness through pure CSS, do not use a framework or library
Connect to an outside API, and display the returned data

The scary thing, is less than 10% get to the 3rd question within 30 minutes. But that doesn't mean they aren't a good candidate. If I see people using arrow functions, chaining functions, using const/let, using the array methods in a good usecase (that they can explain), using flexbox or grid these candidates are up on some modern patterns, and are viable for further look.

Sidenote : at least 2 times we caught someone cheating and have someone else typing their code on a zoom session during covid interviews

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Explain the difference between `undefined` and _not defined_ in JavaScript

In JavaScript if you try to use a variable that doesn't exist and has not been declared, then JavaScript will throw an error `var name is not defined` and the script will stop execute thereafter. But If you use `typeof undeclared_variable` then it will return `undefined`. Before starting further discussion let's understand the difference between declaration and definition. `var x` is a declaration because you are not defining what value it holds yet, but you are declaring its existence and the need of memory allocation. ```javascript var x; // declaring x console.log(x); //output: undefined

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Describe _Closure_ concept in JavaScript as best as you could

Consider: ```js function makeAdder(x) { // parameter `x` is an inner variable // inner function `add()` uses `x`, so // it has a "closure" over `x` function add(y) { return y + x; }; return add; } ``` Reference to inner `add` function returned is able to remember what `x` value was passed to makeAdder function call. ```js var plusOne = makeAdder( 1 ); // x is 1, plusOne has a reference to add(y) var plusTen = makeAdder( 10 ); // x is 10 plusOne(3); // 1 (x) + 3 (y) = 4 plusTen(13); // 10 (x) + 13 (y) = 23 ``` In C and most other common languages, after a function returns, all the

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What is the drawback of creating true private in JavaScript?

One of the drawback of creating a true private method in JavaScript is that they are very memory inefficient because a new copy of the method would be created for each instance. ```javascript var Employee = function (name, company, salary) { this.name = name || ""; //Public attribute default value is null this.company = company || ""; //Public attribute default value is null this.salary = salary || 5000; //Public attribute default value is null // Private method var increaseSalary = function () { this.salary = this.salary + 1000; }; // Public method this.dispalyInc

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