How to round down a number JavaScript [SOLVED]

Introduction

Rounding numbers can be a little frustrating if you don’t know the right method or approach to use for it. You might want to round down your number value, and so the static round method would not suffice.

In this article, we will show you two methods that we can use to round down number values in JavaScript.

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Different method to round down in JavaScript

With the built-in Math object, we can carry out many mathematical operations and rounding is one such. The first method that comes to mind when the idea of rounding numbers is present is the Math.round() method.

Method-1: Using the round method

The Math.round() method rounds its number value argument to the nearest integer based on typical mathematical rounding. So, if the decimal point of the number is greater than or equal to 0.5, it rounds up to the next higher absolute value, but if is lower than 0.5, it rounds down to the lower absolute value. For example, if the number we have is 4.6, it will round up to 5, but if the number is 4.3, it will round down to 4.

const num = 4.56;
const numRounded = Math.round(num);

console.log(numRounded);

Output

5

However, if we need a case where the decimal point of the number is greater than 0.5 or less than 0.5, it should always round down, we need another method, and that’s where the floor and trunc method comes in.

Method-2: Using the floor method

The floor method is also a static method within the Math object, and it rounds down the number value passed to it. So, if you pass 4.99 to the floor method, it would return 4. Let’s show the floor method in action.

const num = 4.98;
const numRounded = Math.floor(num);

console.log(numRounded);

Output

4

With the Math.floor() method, you can round down the number value.

Method-3: Round down using the trunc method

If you want another static Math method, we make use of the trunc method returns only the integer part of a number (as it removes the decimal number). It works by simply splitting the number from the point of the dot, and return the left side (the integer part).

To illustrate we will use the Math.trunc() method on a whole number and a decimal value.

const numOne = 4.98;
const numTwo = 17;

const numOneRound = Math.floor(numOne);
const numTwoRound = Math.floor(numTwo);

console.log(numOneRound, numTwoRound);

Output

4 17

So, with the 4.98, it was round down to 4, and the number 17 was left as it is.

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Summary

To round down numbers in JavaScript, we can make use of two static Math method - floor and trunc - which work in different ways but achieve the set goal.

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References

Math.round() - JavaScript | MDN (mozilla.org)
Math.floor() - JavaScript | MDN (mozilla.org)
Math.trunc() - JavaScript | MDN (mozilla.org)