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Subha Chanda

We all have learned about rounding off numbers in school. We usually increase the integer if its value is >=.5 and decrease it if its value is <= .4.

1.5 ≈ 2

1.4 ≈ 1

JavaScript has a built-in object called **Math** that has properties and methods for mathematical constants and functions.

We have three methods that are mostly used to round off a number in JS, i.e., `Math.ceil()`

, `Math.floor()`

, and `Math.round()`

. Let’s explore them in this article.

The ** Math.ceil function** in JavaScript is used to round up a number that is passed into it to its nearest integer. What do I mean by rounding up? I mean towards the greater value.

`Math.ceil()`

only takes one parameter, the value to be rounded. So, if we have a value of 1.4, `Math.ceil()`

will round off it to 2.console.log(Math.ceil(1.4)); //2 console.log(Math.ceil(1.6)); //2 console.log(Math.round(-1.4)); //-1 console.log(Math.round(-1.6)); //-1

*Photo from Wikipedia*

While the `Math.ceil`

method returns the smallest integer greater than or equal to the value we pass, ** Math.floor** returns the largest or equal integer that is less than the given value. It also takes a single parameter.

*Photo from Wikipedia*

So, if we pass the value 1.4 in `Math.floor`

, we’ll get 1 in return. If we pass 1.6, we’ll also get 1.

console.log(Math.floor(1.4)); // 1 console.log(Math.floor(1.6)); // 1 console.log(Math.floor(-1.4)); // -2 console.log(Math.floor(-1.6)); // -2

** Math.round()** rounds off a number depending on the fractional part of the number. So, if the fractional part is >=.5, it’ll return the smallest integer that is still greater than the passed value. If the number is <=.4, we’ll get the largest possible integer that is still smaller than the number we passed.

console.log(Math.round(1.4)); // 1 console.log(Math.round(1.6)); // 2 console.log(Math.round(1.5)); // 2 console.log(Math.round(-1.4)); // -1 console.log(Math.round(-1.6)); // -2 console.log(Math.round(-1.5)); // -1

So, `Math.round()`

can go both upward and downward depending on the fractional part.

There’s another method available in JS Math object, `Math.trunc()`

. ** Math.trunc()** returns the integer part of a number by removing any fractional part of that number.

console.log(Math.trunc(1.4)); // 1 console.log(Math.trunc(1.6)); // 1 console.log(Math.trunc(-1.4)); // -1 console.log(Math.trunc(-1.6)); // -1

Rounding off numbers is an essential part of programming. I hope this article triggered your memory of the different built-in rounding off methods we have in JavaScript. Leave an ❤ if you found this article helpful. 😊

RELATED TAGS

math.ceil

math.floor

math.round

javascript

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