JavaScript How to Convert Decimal to Binary Easily

Use the JavaScript method number.toString(2) to convert a decimal number to its binary string representation, for example, (10).toString(2) returns '1010'.

Examples

Input5

Output'101'

Input10

Output'1010'

Input0

Output'0'

How to Think About It

To convert a decimal number to binary, think of representing the number in base 2 instead of base 10. JavaScript provides a simple way to do this by converting the number to a string in base 2 using toString(2).

Algorithm

1

Get the decimal number input.

2

Use the built-in method to convert the number to a binary string by specifying base 2.

3

Return or print the binary string.

Code

javascript

const decimalNumber = 10;
const binaryString = decimalNumber.toString(2);
console.log(binaryString);

Output

1010

Dry Run

Let's trace converting decimal 5 to binary using toString(2).

1

Start with decimal number

decimalNumber = 5

2

Convert to binary string

binaryString = (5).toString(2) => '101'

3

Output the result

console.log(binaryString) prints '101'

Decimal Number	Binary String
5	101

Why This Works

Step 1: Using toString with base 2

The toString method converts a number to a string in the specified base, here base 2 for binary.

Step 2: Binary representation

The method returns the binary digits as a string, which is easier to use or display.

Alternative Approaches

Manual division method

javascript

function decimalToBinary(num) {
  let binary = '';
  while (num > 0) {
    binary = (num % 2) + binary;
    num = Math.floor(num / 2);
  }
  return binary || '0';
}
console.log(decimalToBinary(10));

This method shows the step-by-step division by 2 but is longer and less efficient than using toString(2).

Using bitwise operators

javascript

function decimalToBinary(num) {
  return (num >>> 0).toString(2);
}
console.log(decimalToBinary(10));

This uses unsigned right shift to handle numbers safely and then converts to binary string.

Complexity: O(log n) time, O(log n) space

Time Complexity

The conversion depends on the number of bits in the decimal number, which is proportional to log base 2 of the number.

Space Complexity

The output string length grows with the number of bits, so space is also O(log n).

Which Approach is Fastest?

Using toString(2) is fastest and simplest; manual methods are slower and more complex.

Approach	Time	Space	Best For
toString(2)	O(log n)	O(log n)	Quick and easy conversion
Manual division	O(log n)	O(log n)	Learning how binary works
Bitwise operators	O(log n)	O(log n)	Handling unsigned integers