Fullstack Cafe JavaScript Challenges

Rahul Biswas

6 min readMay 16, 2020

10 JavaScript Coding Problems from Fullstack Cafe - Milestone 3 (Day 6)

Today we’ve practiced 25 JavaScript coding interview problems from fullstack.cafe. Here we’ve presented 10 of them.

1. Checking Anagrams of one another

Problems:
Given two strings, return true if they are anagrams of one another.

Solution:

What is Anagram?
An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. For example, the word anagram can be rearranged into nag a ram, or the word binary into brainy or the word adobe into abode.

2. Callback function

Problem:
Explain what a callback function is and provide a simple example.

Solution:
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.

function modifyArray(arr, callback) {
  // do something to arr here
  arr.push(100);
  // then execute the callback function that was passed
  callback();
}

var arr = [1, 2, 3, 4, 5];

modifyArray(arr, function() {
  console.log("array has been modified", arr);
});

The output will be:

3. FizzBuzz Challenge

Problem:
Create a for loop that iterates up to 100 while outputting "fizz" at multiples of 3, "buzz" at multiples of 5 and "fizzbuzz" at multiples of 3 and 5.

Solution:

for (let i = 1; i <= 100; i++) {
  let f = i % 3 == 0,
    b = i % 5 == 0;
  console.log(f ? (b ? 'FizzBuzz' : 'Fizz') : b ? 'Buzz' : i);
}

The output will be:

4. “this” keyword

Problem:
How does the “this” keyword work? Provide some code examples.

Solution:
In JavaScript, this always refers to the “owner” of the function we’re executing, or rather, to the object that a function is a method of.

function foo() {
    console.log( this.bar );
}

var bar = "global";

var obj1 = {
    bar: "obj1",
    foo: foo
};

var obj2 = {
    bar: "obj2"
};

The output will be:

5. Recursive function

Problem:
Write a recursive function that performs a Binary Search

Solution:

function recursiveBinarySearch(array, value, leftPosition, rightPosition) {  if (leftPosition > rightPosition){
         return -1;
  } 
 
  var middlePivot = Math.floor((leftPosition + rightPosition) / 2);
  if (array[middlePivot] === value) {
    return middlePivot;
  } else if (array[middlePivot] > value) {
    return recursiveBinarySearch(array, value, leftPosition, middlePivot - 1);
  } else {
    return recursiveBinarySearch(array, value, middlePivot + 1, rightPosition);
  }
}

The output will be:

6. Closure

Problem:
What is “closure” in javascript? Provide an example?

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Solution:

What is Closure?
A closure is a function defined inside another function (called parent function) and has access to the variable which is declared and defined in parent function scope.
A closure can access:
i) Variable declared in his own scope
ii) Variable declared in parent function scope
iii) Variable declared in global namespace

var globalVar = "abc";

// Parent self invoking function
(function outerFunction (outerArg) { // begin of scope outerFunction
  // Variable declared in outerFunction function scope
  var outerFuncVar = 'x';    
  // Closure self-invoking function
  (function innerFunction (innerArg) { // begin of scope innerFunction
    // variable declared in innerFunction function scope
    var innerFuncVar = "y";
    console.log(         
      "outerArg = " + outerArg + "\n" +
      "outerFuncVar = " + outerFuncVar + "\n" +
      "innerArg = " + innerArg + "\n" +
      "innerFuncVar = " + innerFuncVar + "\n" +
      "globalVar = " + globalVar);
  // end of scope innerFunction
  })(5); // Pass 5 as parameter
// end of scope outerFunction
})(7); // Pass 7 as parameter

The output will be:

7. “delete” operator

Problem:
What will be the output of the following code?

Solution:
The output will be 0. delete operator is used to delete a property from an object. Here x is not an object it's local variable. delete operator doesn't affect local variable.

8. “bind” function

Problem:
When would you use the “bind” function?

Solution:
The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.

A good use of the bind function is when you have a particular function that you want to call with a specific this value. You can then use bind to pass a specific object to a function that uses a this reference.

9. Private Variable

Problem:
How would you create a private variable in JavaScript?

Solution:
To create a private variable in JavaScript that cannot be changed you need to create it as a local variable within a function. Even if the function is executed the variable cannot be accessed outside of the function. For example:

To access the variable, a helper function would need to be created that returns the private variable.

10. Enqueue and Dequeue

Problem:
Implement enqueue and dequeue using only two stacks.

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

var inputStack = []; // First stack
var outputStack = []; // Second stack

// For enqueue, just push the item into the first stack
function enqueue(stackInput, item) {
  return stackInput.push(item);
}

function dequeue(stackInput, stackOutput) {
  // Reverse the stack such that the first element of the output stack is the
  // last element of the input stack. After that, pop the top of the output to
  // get the first element that was ever pushed into the input stack
  if (stackOutput.length <= 0) {
    while(stackInput.length > 0) {
      var elementToOutput = stackInput.pop();
      stackOutput.push(elementToOutput);
    }
  }

  return stackOutput.pop();
}