Junior Developer Central JS Practice Exercise - 22

 

Question: 

Write a Javascript function that accepts a string as a parameter and counts the number of vowels within the string. 

Answer: 

function vowelCount (str) {

  let vowels = /[aeiou]/gi;

  let result = str.match(vowels);

  let count = result.length;

  return count; 

  

  };

> we declare a function 'vowelCount' 

> it has one parameter 'str', which is a string

> we declare a variable 'vowels' and initialize it with the 5 vowels

> the 'g' modifier is used on the 'vowels' variable to perform a global match 

> a global match will find all matches and will not stop after finding the first match

> additionally  the 'i' modifier is used on the 'vowels' variable to perform case insensitive matching

> we declare another variable 'result' and initialize it with the result we get when we use the match () method on the 'str' parameter

> the match() method searches a string for a match against a regular expression and returns the matches as an array object

> we want to match the 'str' with the elements in the 'vowels' variable and store the results in the 'result' array

> we declare another variable 'count' and initialize it with a value we get by using the length property on the array 'result' which will give us the total number of elements in the 'result' array

> we return the 'count' variable

Junior Developer Central JS Practice Exercise - 21

 

Question: 

Write a Javascript function that returns a passed string with letters in alphabetical order. 

Example String:           'javascript' 

Example Output:          'aacijprstv'

Answer: 

function alphaStr (str) {

return str.split('').sort().join('')

}          

> we declare a function 'alphaStr' 

> it has one parameter 'str' 

> we use the split ('') method on the string 'str' to split all the characters in an array

> we then use the sort() method to sort the characters in alphabetical order

> we then use the join('') method to create a string by concatenating all the sorted elements of the array created 

> we return this line of code to get our alphabetically sorted string

Junior Developer Central JS Practice Exercise - 20

 

Question: 

Write a Javascript function that returns true if the provided predicate function returns true for all elements in a collection, false otherwise. 

Answer: 

function checkFunction(arr, fn) {

  for (let i = 0; i < arr.length; i++) {

    if (!fn(arr[i])) {

      return false;

    }

  }

  return true;

}

> we declare a function 'checkFunction' 

> it has two parameters 'arr' & 'fn' 

> we want to return false if 'fn' (which is a function) returns false for even one element in 'arr' (which is an array)

> our function should return true if the function 'fn' returns true for all elements in array 'arr'

> so in order to check the result of the function 'fn' on each and every element of array 'arr' we use the for loop

>  we additionally use the if statement to check the boolean value on each iteration of the for loop

> we return false if the condition is met and the loop is terminated

> we keep the iterations running till all the elements of the array are checked and terminate the loop by returning 'true'

Junior Developer Central JS Practice Exercise - 19

 

Question: 

Write a Javascript program to generate a random hexadecimal color code

Answer: 

function getRandomColor() {

        

        let letters = '0123456789ABCDEF'.split('');

        let color = '#';

        for (var i = 0; i < 6; i++ ) {

            color += letters[Math.round(Math.random() * 15)];

        }

        return color;

    }

> we declare a function 'getRandomColor' 

> it has no parameters

> we create a variable 'letters' 

> it is a string of 16 characters - '0123456789ABCDEF'

> we use the split () method to return an array with 16 array elements

> we declare another variable 'color' 

> its is a string with only the '#' character

> we then create a for loop 

>> initialization - before the loop starts we set our variable i = 0

>> condition - we define the condition for the loop to run ('i' must be less than 6)

>> final expression - at the end of each loop iteration we increment the counter variable

>> understanding the statement in the for loop

>> we want to generate a 6 digit hexadecimal color code with a '#' sign before it

>> that 6 digit hexadecimal code needs to be taken from the array we created 'letters' 

>> we use Math.random() to randomly select any of the 16 array elements

>> since array indexes start from 0, we want a random index number from 0 to 15

>> we use the Math.round() method with Math.random() to get a number with no decimals

>> we use both these methods to select a random index number from the 'letters' array

> we then concatenate the result of the 'for loop iteration' with the 'color' string variable

> the for loop will terminate after the 5th iteration and return the 'color' variable

Junior Developer Central JS Practice Exercise - 18

 

Question: 

Write a Javascript program to convert a comma-separated values (CSV) string to a 2D array. A new line indicates a new row in the array. 

for eg. 

Input: 

const oldString = `abc,def,ghi

jkl, mno, pqr

stu, vwx, yza`;

Output: 

0: (3) ["abc", " def", " ghi"]

1: (3) ["jkl", " mno", " pqr"]

2: (3) ["stu", " vwx", " yza"]

Answer: 

function createArr(str) {

  return str.split('\n').map(row => row.split(','));

}

> we declare a variable 'createArr' 

> it has one parameter 'str' 

> to explain this function, we shall use the input example in the question above 'oldString'

> we first split the 'str' with the split () method that will return an array of substrings

> the split ('\n') method will return a new array which will have three items 

> each of these items is a row from the 'oldString' mentioned above

>> so after split ('\n) we get 

>> 0: ["abc, def, ghi"]

>> 1: ["jkl, mno, pqr"]

>> 2: ["stu, vwx, yza"]

> but we need a 2 dimensional array 

> so we need to split each of the values, in the row, into an array itself

>> like this: 

>> 0: ["abc", " def", " ghi"]

>> 1: ["jkl", " mno", " pqr"]

>> 2: ["stu", " vwx", " yza"]

> in order to further split each of the values into an array itself we use the map() method

> the map() method creates a new array with the results of calling a function for every array element

> the map() method calls the provided function once for each element in an array 

> our aim is to further split the row elements we have, into an array itself 

> so we use the map () method and call a function, that will be called on each value of the 'row' 

> so we will use the split () method on each values of the 'row' and split them by the 'comma'

> like this .map(row => row.split(',')

> this will be a one line code and we shall return the same

Junior Developer Central JS Practice Exercise - 17

 

Question: 

Write a Javascript program to compare two objects to determine if the first one contains the same properties as the second one (which may also have additional properties)

for eg: 

const objA = { a: 1, b: 2, c: 1 }; 

const objB = { a: 1, b: 1, c: 1 };

const objC = { a: 1, b: 1, d: 1 };

Answer: 

function comTwoObj (obj1, obj2) {

const obj2Keys = Object.keys(obj2); 

return Object.keys(obj1).every(key => obj2Keys.includes(key));

}

> we declare a function 'comTwoObj' 

> it has 2 parameters 'obj1' & 'obj2' 

> we want to compare the keys of the two objects 'obj1' & 'obj2' 

> we do not want to compare the values, only the keys

> in our case the 'keys' are: a, b, c & so on

> we want to check if 'obj2' has all the keys of 'obj1' 

> 'obj2' can have additional keys as well, for eg: a, b, c, d, e & so on

> but it should have all the keys of 'obj1' 

> so first we create a variable 'obj2Keys' 

> we initialize it with a value we get by using the Object.keys() method on 'obj2'

> Object.keys() will return an array of a given object's property names or key names

> so our variable 'obj2Keys' will be an array of key names / property names of 'obj2'

> we then want to return true, if 'obj2Keys' includes all the key names of 'obj1' 

> however we cannot compare 'obj2Keys' to 'obj1' as 'obj2Keys' is an array

> so we use the Object.keys() method on 'obj1' as well 

> this method will return an array

> we also add the every() method on Object.keys(obj1)

> like this: Object.keys(obj1).every()

> the every() method returns true if all elements in an array pass a test

> the every method () executes the function once for each element present in the array

> so within the every () method we want to check if the array 'obj2Keys' includes all the elements in the array that is created [ when we use the '' Object.keys(obj1) '' ]

> so we use the includes() method to compare and check the two arrays

> this test will return 'true' if all elements of the array 'Object.keys(obj1) are included in 'obj2Keys'

Junior Developer Central JS Practice Exercise - 16

 

Question: 

Given a year, report if it is a leap year. 

Answer: 

function isLeapYear (year) {

const leapYear01 = year; 

const leapYear02 = leapYear01 / 4;

if (Number.isInteger(leapYear02)) {

return true; 

} else { 

return false;

}

}

> we declare a function 'isLeapYear' 

> it has one parameter 'year' 

> leap year has 366 days

> leap year comes every 4 years

> all leap years are divisible by 4

> hence all the years that are divisible by 4 are 'leap years' 

> so first we create a variable 'leapYear01' 

> we initialize it with a value that we get in 'year' argument

> then we create another variable 'leapYear02' 

> we initialize it with a value that we get by dividing the 'leapYear01' by 4

> we then open an if/else statement

> we want to check if the value stored in 'leapYear02' is an integer

> an integer is a whole number

> an integer is a number that can be written without a fractional component

> our if statement will check if the value is an integer

> if it is an integer, then we want to return true

> if it is not an integer, then we want to return false

> we return false as the value stored is not a whole number and so the value stored in 'leapYear02' is not divisible by 4

> if it is not divisible by 4 then it is not a 'leap year'