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.

Node.js Series Overview

  1. String Replace All Appearances
  2. Remove All Whitespace From a String in JavaScript
  3. Generate a Random ID or String in Node.js or JavaScript
  4. Remove Extra Spaces From a String in JavaScript or Node.js
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  8. How to Check if a Value is a String in JavaScript or Node.js
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  10. Check if a Value is a String in JavaScript and Node.js
  11. Limit and Truncate a String to a Given Length in JavaScript and Node.js
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  24. How to Count Words in a File
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  26. Append Characters or Words to a String in JavaScript or Node.js
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  32. Uppercase the First Character of a String in JavaScript or Node.js
  33. Prepend Characters or Words to a String in JavaScript or Node.js
  34. Check if a String is a Number
  35. Convert a String to Buffer

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!

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