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•By Iqbal Mahmud

10 JavaScript Coding Interview Questions Solve With Code

interview-preparationjavascript-interviewjavascriptinterview-questions

Q-1: Write a function that would allow you to do this

You can create a closure to keep the value of a even after the inner function is returned. The inner function that is being returned is created within an outer function, making it a closure, and it has access to the variables within the outer function, in this case the variable a.

Q-2: Palindrome

A palindrome is a word, sentence or other type of character sequence which reads the same backward as forward. For example, “racecar” and “Anna” are palindromes. “Table” and “John” aren’t palindromes, because they don’t read the same from left to right and from right to left.

Understanding the challenge

The problem can be stated along the following lines: given a string, return true if the string is a palindrome and false if it isn’t. Include spaces and punctuation in deciding if the string is a palindrome. For example:

palindrome('racecar')  ===  true
palindrome('table')  ===  false

Reasoning about the challenge

This challenge revolves around the idea of reversing a string. If the reversed string is the same as the original input string, then you have a palindrome and your function should return true. Conversely, if the reversed string isn’t the same as the original input string, the latter is not a palindrome and your function is expected to return false.

Solution

Here’s one way you can solve the palindrome challenge:

Next, reverse the input string. You can do so by turning the string into an array using the String’s .split() method, then applying the Array’s .reverse() method and finally turning the reversed array back into a string with the Array’s .join() method. I’ve chained all these methods above so the code looks cleaner.

Q-3: FizzBuzz

This is a super popular coding challenge — the one question I couldn’t possibly leave out. Here’s how you can state the problem.

Understanding the challenge

The FizzBuzz challenge goes something like this. Write a function that does the following:

  • console logs the numbers from 1 to n, where n is the integer the function takes as its parameter
  • logs fizz instead of the number for multiples of 3
  • logs buzz instead of the number for multiples of 5
  • logs fizzbuzz for numbers that are multiples of both 3 and 5

Example:

fizzBuzz(5)

Result:

// 1
// 2
// fizz
// 4
// buzz

Reasoning about the challenge

One important point about FizzBuzz relates to how you can find multiples of a number in JavaScript. You do this using the modulo or remainder operator, which looks like this: %. This operator returns the remainder after a division between two numbers. A remainder of 0 indicates that the first number is a multiple of the second number:

12 % 5 // 2 -> 12 is not a multiple of 5
12 % 3 // 0 -> 12 is multiple of 3

If you divide 12 by 5, the result is 2 with a remainder of 2. If you divide 12 by 3, the result is 4 with a remainder of 0. In the first example, 12 is not a multiple of 5, while in the second example, 12 is a multiple of 3.

With this information, cracking FizzBuzz is a matter of using the appropriate conditional logic that will lead to printing the expected output.

Solution

Here’s one solution you can try out for the FizzBuzz challenge:

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Q-1: Write a “mul” function which will properly when invoked as below syntax.

Here mul function accept the first argument and return anonymous function which take the second parameter and return anonymous function which take the third parameter and return multiplication of arguments which is being passed in successive

In JavaScript function defined inside has access to outer function variable and function is the first class object so it can be returned by function as well and passed as argument in another function.

  • A function is an instance of the Object type
  • A function can have properties and has a link back to its constructor method
  • Function can be stored as variable
  • Function can be pass as a parameter to another function
  • Function can be returned from function

Q-5: Implement enqueue and dequeue using only two stacks

Enqueue means to add an element, dequeue to remove an element.

Q-6: Given a string, reverse each word in the sentence

For example Welcome to this Javascript Guide! should be become emocleW ot siht tpircsavaJ !ediuG

Q-7: How to empty an array in JavaScript?

How could we empty the array above?

Method 1

Above code will set the variable arrayList to a new empty array. This is recommended if you don't have references to the original array arrayList anywhere else because It will actually create a new empty array. You should be careful with this way of empty the array, because if you have referenced this array from another variable, then the original reference array will remain unchanged, Only use this way if you have only referenced the array by its original variable arrayList.

Method 2

Above code will clear the existing array by setting its length to 0. This way of empty the array also update all the reference variable which pointing to the original array. This way of empty the array is useful when you want to update all the another reference variable which pointing to arrayList.

Method 3

Above implementation will also work perfectly. This way of empty the array will also update all the references of the original array.

Method 4

Above implementation can also empty the array. But not recommended to use often.

Q-8: How would you use a closure to create a private counter?

You can create a function within an outer function (a closure) that allows you to update a private variable but the variable wouldn’t be accessible from outside the function without the use of a helper function.

Q-9: Write a function that would allow you to do this.

You can create a closure to keep the value passed to the function createBase even after the inner function is returned. The inner function that is being returned is created within an outer function, making it a closure, and it has access to the variables within the outer function, in this case the variable baseNumber.

Q-10: Explain what a callback function is and provide a simple example.

A callback function is a function that is passed to another function as an argument and is executed after some operation has been completed. Below is an example of a simple callback function that logs to the console after some operations have been completed.

10 JavaScript Coding Interview Questions Solve With Code was originally published in The Startup on Medium, where people are continuing the conversation by highlighting and responding to this story.