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  3. JavaScript — Check if a Number Is Infinity

JavaScript — Check if a Number Is Infinity

We recently worked on an audio player in a web application. The player uses a streaming server to play tracks. For example, a track can be a radio song, a podcast episode, or an endless radio stream.

An audio track and podcast episodes are finite. Finite tracks should use a progress bar to show the listening time. But the progress bar should not be visible for endless radio streams. And radio streams have a duration of „infinity“.

This tutorial shows you how to detect whether a given number is (positive or negative) infinity.

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Detect if a Number Evaluates to Infinity

JavaScript’s global Number object provides a handful of static methods. One of these methods is Number#isFinite determining whether a given number is finite or not. You can use this helper method to constructor your own isInfinity method like this:

/**
 * Determine whether the given `number` evaluates to infinity.
 * 
 * @param {any} number
 * 
 * @returns {Boolean}
 */
function isInfinity(number) {  
    return !Number.isFinite(number)
}

Then use your isInfinity helper method to detect whether a number equals infinity:

isInfinity(1 / 0)  
// true

isInfinity(10 / 2)  
// false

isInfinity(0 / 0)  
// true

Positive or Negative Infinity

You may also distinguish between positive and negative infinity. JavaScript’s global Number object provides constants you can use for comparison:

const isPositiveInfinity = (1 / 0) === Number.POSITIVE_INFINITY  
// true

const isPositiveInfinity = (-1 / 0) === Number.POSITIVE_INFINITY  
// false

const isPositiveInfinity = (-1 / 0) === Number.NEGATIVE_INFINITY  
// true

Enjoy infinity!

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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