How to Accurately Round Numbers to Two Decimal Places in JavaScript?

Rounding Numbers to Two Decimal Places When Necessary

When handling numerical data, it's often necessary to round values to specified decimals. However, in some cases, we only want to round if the value is not already rounded to the desired precision.

Consider the following scenario: you want to round numbers to at most two decimal places, but only if necessary. For example:

Input:
10
1.7777777
9.1

Output:
10
1.78
9.1

Using Math.round()

One possible solution is to use the Math.round() method:

let roundedNum = Math.round(num * 100) / 100;

This approach multiplies the number by 100 before rounding it to an integer (effectively shifting the decimal point two places to the right) and then divides it back by 100 to get the value with two decimal places.

Using Number.EPSILON

However, this approach doesn't handle borderline cases correctly. For instance, 1.005 would round to 1.01 instead of 1.00. To address this, we can use Number.EPSILON:

let roundedNum = Math.round((num + Number.EPSILON) * 100) / 100;

Number.EPSILON represents the smallest difference between two floating-point numbers that is considered significant. Adding it to the number ensures that the value is rounded correctly, even in borderline cases.

The above is the detailed content of How to Accurately Round Numbers to Two Decimal Places in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!