How to check if a number evaluates to Infinity using JavaScript?

In JavaScript, when we divide any number by zero, we get the infinity value. Also, developers can make a mistake in writing mathematical expressions which evaluate to Infinity. Before performing any operation with the returned value from mathematical expressions, we need to check if the number value is finite.

Here, we will learn three approaches to check if a number evaluates to Infinity using JavaScript.

Comparing with Number.POSITIVE_INFINITY and Number.NEGATIVE_INFINITY

In JavaScript, the Number object contains POSITIVE_INFINITY and NEGATIVE_INFINITY properties that represent positive and negative infinity values. We can compare our numerical value with these properties to check if the number evaluates to Infinity.

Syntax

if (num == Number.POSITIVE_INFINITY || num == Number.NEGATIVE_INFINITY) {
   // number is infinite
} else {
   // number is finite
}

Example

In this example, we define two numbers with different values. The checkNumberIsFinite() function takes the number value as a parameter and prints whether the number is finite or infinite.

   
Comparing the number value with Number.POSITIVE_INFINITY and Number.NEGATIVE_INFINITY to check if number evaluates to Infinity.
   
   

Using the Number.isFinite() Method (Recommended)

The Number.isFinite() method takes a numeric value as a parameter and returns a boolean value based on whether the number is finite. This is the most reliable approach for checking if a number evaluates to Infinity.

Syntax

if (Number.isFinite(num)) {
   // number is finite
} else {
   // number evaluates to infinite or NaN
}

Parameters

• num ? The number to evaluate.

Return Value

• It returns a Boolean value: true if the number is finite, false if it's infinite or NaN.

Example

We use the Number.isFinite() method as a condition in the if-else statement. The method returns true or false based on the number value we pass as a parameter.

   
Using the Number.isFinite() method to check if number evaluates to Infinity.
   
   

Using Math.abs() Method and Infinity Keyword

The Math.abs() method returns the absolute value of any number. Infinity is a JavaScript keyword that represents the infinity value. We can take the absolute value of the number and compare it with Infinity.

Syntax

let number = Math.abs(num);
if (number == Infinity) {
   // num is infinite
} else {
   // num is finite
}

Example

The example below contains the evaluateNumber() function, which converts the number value to its absolute value and compares it with the Infinity keyword.

   
Using the Math.abs() method and Infinity keyword to check if number evaluates to Infinity.
   

   Evaluate number
   

Comparison of Methods

Conclusion

The best way to check if a number evaluates to Infinity is using the Number.isFinite() method, as it's the most reliable and handles edge cases like NaN. However, all three approaches are valid depending on your specific requirements.