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  3. Check If a Number has Decimal Places in JavaScript or Node.js

Check If a Number has Decimal Places in JavaScript or Node.js

Sometimes you’re running into use-cases where you need to detect whether a given number has decimal places. This tutorial shows you how to do that!

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Detect If a Number Has Decimal Places

Generally, you may want to apply formatting on numbers. And you may want to round numbers having decimal places before formatting. Here’s a utility method helping you to detect whether a given number has decimal places:

/**
 * Determine whether the given `num` has decimal places.
 *
 * @param {Number} num
 *
 * @returns {Boolean}
 */
function hasDecimalPlaces (num) {  
  return !Number.isSafeInteger(num)
}

Please notice: JavaScript comes with precision limits on floating-point numbers. For example, you would expect a number like 3.0000000000000001 to have decimal places. But JavaScript treats this number as an integer. That’s the reason the hasDecimalPlaces utility returns false.

Why not Use Number.isInteger?

The reason we don’t use Number.isInteger is that this method accepts integers that are out of range. That means isInteger would return true for numbers out of range, even though they are not integers.

Enjoy!

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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