How to Convert a Decimal to Hexadecimal in JavaScript

You don’t need to be a math whiz to be a good programmer, but there are a handful of mathematical concepts to learn to help you understand how computers work and set yourself up for success in interviews. In this tutorial, you will learn how to convert a decimal to any base between binary and hexadecimal using a Stack data structure with examples in JavaScript.

Retrieval Practice

• What’s a stack?
• What’s a base?
• How do you convert a decimal to binary?

What’s a Stack?

A stack is a data structure that follows the Last In First Out principle (LIFO). We can only add or remove elements from the top of the stack .

If you want to go deeper, check out JavaScript Stack Data Structure.

What’s a Base?

A base is the number of different digits used to count in a numerical system. We count in base 10 most likely due to us evolving ten fingers. When we count in base 10, we use ten distinct whole numbers.

How to Convert a Decimal to Binary

To understand how to convert a decimal to base, it’s useful to first understand how to convert a decimal to binary. Binary is base 2. We have two different digits to count with, 0 and 1. (Or true and false).

To calculate a binary value, we need to divide the decimal by 2 until the quotient is zero. We store the remainder of each division operation and use that to create a string representing the base.

If you want to go deeper, check out How to Convert a Decimal to Binary in JavaScript

Let’s Get Meta 🧠

Ask yourself the following questions and keep them back of mind as you proceed:

• How do you build something out of nothing?
• How do we count using a base greater than 10?
• Why do I need to know this?

How to Convert Decimal to Base

If converting a decimal to binary is simply a process of repeatedly dividing the decimal by 2 and using the remainder to build a string, how do you think we convert a decimal to any base?

What’s the pattern?

We divide the decimal by the base!

Let’s convert 2048 to base-16, hexadecimal. To do that, though, we need to answer the question posed above: how do we count using a base greater than 10?

What is a number?

It’s a symbol representing a value.

What is 1?

A symbol representing the value one.

What is ‘one’?

A symbol representing the value 1. (And round and round we go…)

What is 10?

In the decimal, or base-10, numeral system, it’s a value represented by two symbols. Because it’s two symbols, we can’t use it in base-16. What’s the solution? More symbols!

Hexadecimal, or base-16, uses the first six characters of the Roman alphabet to represent the values of 10 through 15.

If we wanted to create our own base, say, Emojidecimal, we could use whatever symbols we want:

The symbol doesn’t matter, as long as we all agree on the value that it represents. Do you think Emojidecimal will gain traction? 🤔

Let’s convert 2047 to hexadecimal. The first step is to get the remainder of our dividend and divisor.

2048 % 16 = 15

Our remainder is 15, but we are no longer using base-10, so we can’t add this value to our hexadecimal string. If we use the table we created above, we can see that 15 maps to F, so we start building our hexadecimal string with it, giving us:

F

The next step is to divide:

2048 / 16 = 127

Our quotient is 127, so we repeat the operations above:

127 % 16 = 15

Our remainder is again 15, so we add F to our hexadecimal string, giving us:

FF

We then divide 127 / 16. Our quotient is 7, so we calculate the remainder and divide 7 by 16:

7 % 16 = 7
7 / 16 < 0

Our remainder is 7, so we add it to our hexadecimal string, giving us:

7FF

How to Convert Decimal to Hexadecimal and any Base In-Between Using a Stack in JavaScript

Let’s refactor the algorithm we created in How to Convert a Decimal to Binary in JavaScript to convert any base between binary and hexadecimal using a stack. If you’re unfamiliar with stacks, you may want to first read JavaScript Stack Data Structure.

To calculate a base, we need to divide the decimal by the desired base until the quotient is zero. We store the remainder of each division operation and use that to create a string representing the base.

const decimalToBase = (num, base) => {
  const stack = new Stack();

  const digits = '0123456789ABCDEF';

  let result = '';
  
  while (num > 0) {
    stack.push(num % base);
    num = Math.floor(num / base);
  }
  
  while (stack.top > 0) {
    result += digits[stack.pop()];
  }

  return result;
}

What’s happening here?

We first use our Stack class to declare a new stack.

We then declare a string, digits, representing the 16 symbols in our hexadecimal series.

We next declare an empty string, result, which we will use to build our return value.

We next declare two while loops.

The first while loop iterates over the value of our algorithm parameter, num. In each iteration, we use the modulo operator, %, to get the remainder of num divided by base and push() it to the stack. We then reassign the value of num to the current value of num divided by base. But! We use floor() to round it down. Why? We want to work with whole numbers and we are most interested in our remainder.

🔑 When the value of num is less than zero, we move on to the second while loop, which iterates over the stack. We use the pop() method to remove each value from the top of the stack and build our result string by looking up its associated value in digits.

If we don’t want to use a Stack, we could simply concatenate a string, then reverse it:

const decimalToBase = (num, base) => {

  const digits = '0123456789ABCDEF';

  let result = '';
  
  while (num > 0) {
    result += digits[num % base];
    num = Math.floor(num / base);
  }

  return result.split('').reverse().join('');
}

But the split() converts the string to an array, so we could just start with an array instead and use unshift() rather than reverse() (J4F):

const decimalToBase = (num, base) => {

  const digits = '0123456789ABCDEF';

  let result = [];
  
  while (num > 0) {
    result.unshift(digits[num % base]);
    num = Math.floor(num / base);
  }

  return result.join('');
}

Or we could just cheat and use the built-in toString() method and pass it our base as an argument, meaning we want to convert our string to the given parameter. For example:

const decimalToBase = (num, base) => num.toString(base);

But what fun is that?

Reflection

• How do you build something out of nothing?
• How do we count using a base greater than 10?
• Why do I need to know this?

How Do You Build Something Out of Nothing?

Form patterns! If you want to go deeper, check out my article Pattern Forming and Problem Solving.

How Do We Count Using a Base Greater Than 10?

Hexadecimal, or base-16, uses the first six characters of the Roman alphabet to represent the values of 10 through 15.

Why Do I Need to Know This?

You don’t need to be a math whiz to be a good programmer. But there are a handful of mathematical concepts to learn to help you understand how computers work and set yourself up for success in interviews.

In this tutorial, you learned how to convert a decimal to hexadecimal and any base in-between binary and using a Stack data structure with examples in JavaScript.

Want to level up your problem solving skills? I write a weekly newsletter about programming, problem solving and lifelong learning. Join now