JavaScript Round to 2 Decimal: 5 Secrets to Perfect Rounding!

JavaScript round to 2 decimal places means rounding off the provided decimal number to 2 decimal places. For example, round the 2.335 to 2 decimal places. Which produces the output: 2.34. Clear?

Rounding numbers in JavaScript is both very easy and, on the other hand, very difficult! But JavaScript provides us with a range of methods to deal with the number formatting issue. Each method has its own unique pros and cons.

Bulit in JS methods like Math.round(), Math.ceil(), and Math.floor(), rounding numbers to the nearest whole number. Moreover, we have to take different approaches apart from JS-inplaced math rounding methods for different cases to achieve rounding to two decimal places.

Don’t worry; in this article, we will discuss all possible issues along with their workable solutions. Just bear with us till the end of the article. We hope you will learn a lot instead of formatting only a number!

Importance of Precision in Number Handling

As a developer, you have definitely made a lot of changes, even after the successful completion of your project. Sometimes reports are populated without decimal points or with more decimal places. Right?

Business reports are very sensitive, and the top-level management won’t allow undefined formatting.

So what do we understand? We understand that, from transactional data or statistical data to scientific data, everywhere rounding numbers are a must.

But why do we need to round to two decimal places exactly? Because this format is the most acceptable monetary format worldwide, It balances a number with accuracy and presentability.

JavaScript Round to 2 Decimal Places: Use Inbuilt Function toFixed()

The JavaScript built-in toFixed() method rounds a number to a specific number of decimal places. Apply the method to the numbers only, and in return, receive a rounded number in the form of a string. Not a number. Later, we can convert the returned string to a numeric value if required.

We can call the toFixed() method for a number data type only, and it takes a single parameter that determines the number of decimal places in return.

Following is the syntax of the JS toFixed() method:

number.toFixed(x)

Where ‘number’ is the number to be rounded, and ‘x’ is the desired number of decimal places.

Let’s do an example using it:

<script>

   var num1 = 2.378204;
   var num2 = 2.378204;
   var num3 = 2.378204;
   var num4 = 2.378204;
   var num5 = 2.3;

   // Removal decimal part
   var result1 = num1.toFixed();
   //// Removal decimal part
   var result2 = num2.toFixed(0);
   var result3 = num3.toFixed(1);
   // javascript round to 2 decimal
   // javascript to round to 2 decimal places
   var result4 = num4.toFixed(2);
   // Number of decimal places is higher than the number
   // zeros are added
   var result5 = num5.toFixed(3);

   console.log(result1);
   console.log(result2);
   console.log(result3);
   console.log(result4);
   console.log(result5);

   // Now check the datatype of toFixed method of var result4
   console.log(typeof result4)

   // Now convert to number from string
   console.log(typeof parseFloat(result4)+':'+parseFloat(result4))

</script>

Output

Code Explanation: JS Round to 2 Decimal

In this example, we first apply the toFixed() method without mentioning the parameter. So the method removes all decimal values. Later on, we test the method by increasing the required decimal places. And received the outputs as expected.

But there is one issue. The toFixed() method always returns a string output, not a numeric value. So, you have to carefully handle the return type and convert the type as per your requirements.

Here in this example, we convert the toFixed() method string return type to a float type and log everything for better understanding.

JavaScript to Round to 2 Decimal Places: Using the Math.round() Function

There is another function in JS called Math.round(). This method rounds a given number to specific decimal places. 

The math.round() method also takes an argument like the isFixed() method but returns a numeric value, not a string. So that post-conversion is not mandatory here.

One more important point is that we cannot directly use the Math.round() static function; rather, we have to first multiply the number by 100 and then pass it to the round() method. After that, we must divide the result by 100 to get our required decimal places.

Code Example

<script>

   // numbers slightly varied after point
   // to understand floor & ceil effect
   // of round function
   var num1 = 2.378204;
   var num2 = 2.578204;
   var num3 = 2.378204;
   var num4 = 2.372204;
   var num5 = 2.378504;

   var result1 = Math.round(num1);
   var result2 = Math.round(num2*10)/10;

   // JavaScript round to 2 decimal places
   // use 100 as multiplier & divider
   var result3 = Math.round(num3*100)/100;

   // JavaScript round to 3 decimal places
   // use 1000 as multiplier & divider
   // and so on
   var result4 = Math.round(num4*1000)/1000;
   
   // First decimal number is 3 
   // So works like floor
   console.log(result1)

   // First decimal number is 3 
   // So works like ceil
   // Compare other output this way
   console.log(result2)
   console.log(result3)
   console.log(result4)
   console.log(typeof result1)

</script>

Output

Use Number.EPSILON: More Accurate Precision

The Math.round() function does not work well in some scenarios. Not only this function but also all JS rounding functions fail in certain cases due to base2 representations in memory, such as numbers like 0.1 or 0.01. Don’t worry, we will discuss a lot about it after discussing all JS rounding functions.

But we would like to mention a simple workaround to fix the Math.round() function rounding issues. It will also not work in all scenarios, but it is good to know as an alternative option.

EPSILON is a static property of a number, so you must use it as a number. EPSILON. Not as a property of a number value.

Here is a case study with JS Math.round() function with and without EPSILON. Check below:

<script>

   // numbers slightly varied after point
   // to understand floor & ceil effect
   // of round function

   // number .005 ==> .095 are problemetic for rounding
   // check .005 ==> .035 combination for all methods also
   // for tofix() method check upto .095

   var num1 = 1.005;
   var num2 = 1.005;
   var num3 = 1.015;
   var num4 = 1.025;
   var num5 = 1.035;

   var result1 = Math.round(num1);
   var result1_EPSILON = Math.round(num1+Number.EPSILON);

   // JavaScript round to 2 decimal places
   // use 100 as multiplier & divider
   var result2 = Math.round(num2*100)/100;
   var result2_EPSILON = Math.round((num2+Number.EPSILON)*100)/100;

   var result3 = Math.round(num3*100)/100;
   var result3_EPSILON = Math.round((num3+Number.EPSILON)*100)/100;

   var result4 = Math.round(num4*100)/100;
   var result4_EPSILON = Math.round((num4+Number.EPSILON)*100)/100;

   var result5 = Math.round(num5*100)/100;
   var result5_EPSILON = Math.round((num5+Number.EPSILON)*100)/100;

   console.log('ROUND: '+result1+'  WITH EPSILON:'+result1_EPSILON);
   console.log('ROUND: '+result2+'  WITH EPSILON:'+result2_EPSILON);
   console.log('ROUND: '+result3+'  WITH EPSILON:'+result3_EPSILON);
   console.log('ROUND: '+result4+'  WITH EPSILON:'+result4_EPSILON);
   console.log('ROUND: '+result5+'  WITH EPSILON:'+result5_EPSILON);

</script>

Output:

Math.round() and Math.pow()

In Javascript round to 2 decimal places, we can use the Math.round() function with Math.pow(). This combination offers us another solution to rounding to 2 decimal places, or whatever.

<script>

   function toRound(num, precision) {
      var mathFactor = Math.pow(10, precision);
      return Math.round(num * mathFactor) / mathFactor;
   }

   // javascript to round to 2 decimal places
   var result = toRound(2.378204, 2);
   var result2 = toRound(2.378204, 3);

   console.log(result) // Outputs: 2.38
   console.log(result2) // Outputs: 2.378

</script>

Rounding with Intl.NumberFormat

The Intl.NumberFormat object enables language-sensitive number formatting. This static method returns an array containing the user’s full locale information. It’s a very powerful method to build international JS applications.

The constructor formats the number based on the given locale or region. If you don’t supply a locale, it will format the number only with commas. Using a new keyword is not mandatory.

<script>

   var num1 = 1.005;
   var num2 = 1.015;
   var num3 = 1.025;
   var num4 = 1.035;

   // javascript to round to 2 decimal places
   var roundingNum = new Intl.NumberFormat('en-US', {
      style: 'decimal',
      maximumFractionDigits: 2
   })

   var result1 = roundingNum.format(num1);
   var result2 = roundingNum.format(num2);
   var result3 = roundingNum.format(num3);
   var result4 = roundingNum.format(num4);

   // JS round to 2 decimal
   console.log(result1) // Output: 1.01 
   console.log(result2) // Output: 1.02
   console.log(result3) // Output: 1.03
   console.log(result4) // Output: 1.04

</script>

you can customize the locale as per your need.

Custom Rounding Function

The below manual function works perfectly. This function did not show the limitations for base2 issues like other in-built JS solutions. By using this solution, you can rectify the rounding errors, but you may face issues with fixed decimal places. If you are all interested in knowing, please write to us; we will surely provide a workaround.

<script>

   function roundingNum(num, precission) {
   return +(Math.round(num + "e+"+precission) + "e-"+precission);
   }

   
   var num1 = 1.005;
   var num2 = 1.015;
   var num3 = 1.025;
   var num4 = 1.035;

   // javascript round to 2 decimal
   // you can change the presission
   var result1 = roundingNum(num1,2);
   var result2 = roundingNum(num2,2);
   var result3 = roundingNum(num3,2);
   var result4 = roundingNum(num4,2);

   // This experiment shows output
   // like EPSILON
   // JS round to 2 decimal
   console.log("1.005:", result1); // 1.01
   console.log("1.015:", result2); // 1.02
   console.log("1.025:", result3); // 1.03
   console.log("1.035:", result4); // 1.04

</script>

In this code example of the above user-defined function, we used an exponent. Which rounds the number as per the defined precision. If you look at our code, you will find an expression like “e+2,” where 2 is used for 2 decimal places.

Problems with Rounding Numbers in JavaScript

There are some considerations you have to take into consideration when doing rounding in your JS code. A computer always stores binary data only in physical or logical memory locations. Whereas JavaScript stores numbers in 32-bit single-precision binary values.

That’s why some base 10 numbers can’t be accurately stored in base 2, which causes this sort of truncating issue and produces inappropriate results.

Which Methods Should I Use for Rounding Numbers?

So. Now the ultimate question is which JavaScript function we should use for rounding a number up to 2 decimal places? Here we have discussed almost 5 approaches that you can consider. Let’s start our discussion to make our decision right always.

If you just want to round a number to its nearest numeric value, you can use the Math.round function.

But you can consider Math.floor or Math.ceil if you want to round down or up positive numbers. In the case of negative numbers or both, you must use Math.trunc.

If you need to round a number with specific decimal places for producing significant figures, use the Number.toFixed method. But be aware that this method is called by a number, but it returns a string. So we will need another numeric conversion for further calculations.

When to Use?

Developers mostly asked how and why javascript round to 2 decimal? The how part we have already covered in details now we are going discuss the why part.

We know that JavaScript consider up to 15 decimal points while doing arithmetic operations. So seeing a number in a business report or presentations with 15 decimal points is a bit ugly. But for research purpose researchers don’t even want to truncate the last decimal digit for accuracy.

So why is a is a javascript round to two decimal places required? It’s mainly required for:

1. Report generation
2. Data visualizations
3. High-level presentations
4. Space optimization for UI
5. Chart reading
6. Avoid data congestion.

Best Practices: JavaScript to Round to 2 Decimal Places

The best practices and thumb rules are:

1. For rounding down, use the Math.floor() function.
2. For rounding up, use the Math.ceil() function.
3. For rounding to the nearest even number, use the Math.round() function. Include the EPSILON static property, as discussed earlier.
4. For removing the fractional part of a number, use the Math.trunc() function.
5. For rounding up to x decimal places, use the toFixed() function.
6. For unique user requirement fulfillment, use the custom function.

So these are our listed recommendations. And keep all points in mind while rounding a number in JavaScript.

Conclusion

From the above discussions, we came to know every aspect of how JavaScript rounding to two decimal places works. We have discussed all the built-in JS functions like toFixed(), Math.roud(), etc. We also discussed how to create a custom function to 2 decimal places.

We discussed why “JavaScript round to 2 decimal” is required and all of its best practices. So, don’t be confused. Keep coding and stay with us.

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