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Programs

How to Convert Decimal to Binary in JavaScript

written by programmerdude

In this article we show a simple way to convert a decimal number to a binary number using JavaScript

Example 1

The user is prompted to enter a number.

The parseInt() method is used to convert a string value to an integer and we store this as a constant

We then use the toString method which allows you to specify a number base

// convert decimal to binary

// take input
const number = parseInt(prompt('Enter a decimal number: '));

// convert to binary
const result = number.toString(2);

console.log('Binary:' + ' ' + result);

We then input the number 15 like this

When you run this you will see something like this

Binary: 1111
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Programs

Display All Prime Numbers between 1 and 100 in JavaScript

written by programmerdude

In this example we display all the prime numbers between 1 and 100.

A prime number is a positive integer that is only divisible by 1 and itself

Example

// program to print prime numbers between 1 and 100
console.log(`The prime numbers are:`);

// looping from 1 to 100
for (let i = 1; i <= 100; i++) 
{
    let flag = 0;

    // looping through 2 to number
    for (let j = 2; j < i; j++) 
	{
        if (i % j == 0) 
		{
            flag = 1;
            break;
        }
    }

    // if number greater than 1 and not divisible by other numbers
    if (i > 1 && flag == 0) 
	{
        console.log(i);
    }
}

This will display the following

The prime numbers are:
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
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Programs

How to Check if its a Leap Year in JavaScript

written by programmerdude

In this example we check if a year is a leap year

Some examples use a formula to check if a year is a leap year, this example checks if the month of February contains 29 days in the year specified

Example 1

// program to check leap year
function checkLeapYear(year) 
{

    const leap = new Date(year, 1, 29).getDate() === 29;
    if (leap) 
	{
        console.log(year + ' is a leap year');
    } 
	else 
	{
        console.log(year + ' is not a leap year');
    }
}

// remove comment to take input
// const year = prompt('Enter a year:');
checkLeapYear(2000);
checkLeapYear(2002);
checkLeapYear(2004);

 

When you run this you will see something like this

2000 is a leap year
2002 is not a leap year
2004 is a leap year

You can remove the comment to take user input like this

 

// program to check leap year
function checkLeapYear(year) 
{

    const leap = new Date(year, 1, 29).getDate() === 29;
    if (leap) 
	{
        console.log(year + ' is a leap year');
    } 
	else 
	{
        console.log(year + ' is not a leap year');
    }
}

// remove comment to take input
const year = prompt('Enter a year:');
checkLeapYear(year);

 

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Programs

How to Display the Current Date in JavaScript

written by programmerdude

In this example we will display the current date and time in JavaScript

Example 1

// get local machine date time
const date = new Date();

// get the date as a string
const datenow = date.toDateString();

// get the time as a string
const time = date.toLocaleTimeString();

// display date
console.log('Date: ' + datenow);

// display time
console.log('Time: ' + time);

 

When you run this you will see something like this

Date: Wed Apr 13 2022
Time: 7:14:48 PM
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Programs

Compare Two Strings using RegEx in JavaScript

written by programmerdude

In this example we will check that two strings match

You will see that the pattern below has the following gi, this means

Flags Description
g Performs a global match (find all matches)
i Performs case-insensitive matching

Example 1

// string comparison
const string1 = 'maxJavascript Programs';
const string2 = 'maxjavascript programs';

// create regex
const pattern = new RegExp(string1, "gi");

// compare the stings
const result = pattern.test(string2)

if(result) 
{
    console.log('The strings are the same.');
} 
else 
{
    console.log('The strings are not the same.');
}

When you run this you will see something like this

The strings are similar.
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Programs

How to Compare Two Strings in JavaScript

written by programmerdude

In this example we will compare 2 strings to see if they are a match

Example 1

First of all we convert the strings to lowercase using .toLowerCase() method, you can also convert to uppercase if you preferred using the toUpperCase() method.

We then compare these 2 strings using the strict equality operator ===

Depending on the result we display some text to the user

// string comparison
const string1 = 'maxJavascript Programs';
const string2 = 'maxjavascript programs';

// compare both strings
const result = string1.toLowerCase() === string2.toLowerCase();

if(result) 
{
    console.log('The strings are similar.');
} 
else 
{
    console.log('The strings are not similar.');
}

When you run this you will see something like this

The strings are similar.

Example 2

But what if you did not convert the string to lowercase or uppercase

// string comparison
const string1 = 'maxJavascript Programs';
const string2 = 'maxjavascript programs';

// compare both strings
const result = string1 === string2;

if(result) 
{
    console.log('The strings are similar.');
} 
else 
{
    console.log('The strings are not similar.');
}

When you run this you will see something like this

The strings are not similar.

It all depends whether you want to check for case sensitivity or not, especially important when taking user input.

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Programs

Replace All Occurrence of String Using RegEx in JavaScript

written by programmerdude

In this example we will replace a string in another string using JavaScript

This time will use regular expressions

We will define a string, then we will define t he word we want to replace and then use string.replace to replace that string with another one.

You will see that the regex below has the following /gi, this means

Flags Description
g Performs a global match (find all matches)
i Performs case-insensitive matching

Example 1

We are replacing the word red with blue

// replace all occurrence of a string
const string = 'A red bird was sitting on a red fence, is it a redpoll';

// regex expression
const regex = /red/gi;

// replace the characters
const newText = string.replace(regex, 'blue');

// display the result
console.log(newText);

When you run this you will see something like this

A blue bird was sitting on a blue fence, is it a bluepoll
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Programs

How to Generate Random Strings in JavaScript

written by programmerdude

In this example we show you how to generate random strings in JavaScript

Example 1

We will define a list of characters which will include lower and upper case A – Z characters and numbers 0 – 9

// program to generate random strings
const characters ='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';

function generateString(length) 
{
    let result = ' ';
    const charactersLength = characters.length;
    for ( let i = 0; i < length; i++ ) 
    {
        result += characters.charAt(Math.floor(Math.random() * charactersLength));
    }

    return result;
}

console.log(generateString(10));
console.log(generateString(10));
console.log(generateString(10));

 

When you run this you will see something like this, here are 3 runs as above

RUqq56A3QU
dlxHceRtCe
gXVhZMQCp3
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Programs

How to Display a Multiplication Table in JavaScript

written by programmerdude

In  this example we will show you how to generate a multiplication table

Example 1

We take the user input and store in the constant number

We then use a for loop to loop from 1 to 10

We then display the multiplication table multiplying the number the user inputted from 1 to 10

// generate a multiplication table
// get user input
const number = parseInt(prompt('Enter an integer: '));

//create the multiplication table
for(let i = 1; i <= 10; i++) 
{
    // multiply i with user number
    const result = i * number;
    // display the result
    console.log(`${number} * ${i} = ${result}`);
}

When you run this you will see something like this, this was with user input of 5

5 * 1 = 5
 5 * 2 = 10
 5 * 3 = 15
 5 * 4 = 20
 5 * 5 = 25
 5 * 6 = 30
 5 * 7 = 35
 5 * 8 = 40
 5 * 9 = 45
 5 * 10 = 50

Example 2

A slight tweak to the above to allow the user to select the range as well

// generate a multiplication table
// take number input from the user
const number = parseInt(prompt('Enter an integer: '));

// get the range from the user
const range = parseInt(prompt('Enter a range: '));

//create a multiplication table
for(let i = 1; i <= range; i++) 
{
    const result = i * number;
    console.log(`${number} * ${i} = ${result}`);
}
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Programs

How to Check if a Number is Odd or Even in JavaScript

written by programmerdude

Even numbers are those numbers that are exactly divisible by 2.

The remainder operator % will give the remainder when used with a number.

Example 1

// program to check if the number is even or odd
// take input from the user
const number = prompt("Enter a number: ");

//check if the number is even
if(number % 2 == 0) 
{
    console.log("The number is even.");
}
// if the number is odd
else 
{
    console.log("The number is odd.");
}

When you run this you will see something like this

And the output was

The number is odd.

Example 2

You can also use the ternary operator like this

// program to check if the number is even or odd
// take input from the user
const number = prompt("Enter a number: ");

// ternary operator
const result = (number % 2  == 0) ? "even" : "odd";

// display the result
console.log(`The number is ${result}.`);
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