How to Check if a Value is a Number in JavaScript ?
Last Updated : 26 Apr, 2025
To check if a value is a number in JavaScript, use the typeof operator to ensure the value's type is 'number'. Additionally, functions like Number.isFinite() and !isNaN() can verify if a value is a valid, finite number.
Methods to Check if a Value is a Number
There are various ways to check if a value is a number in JavaScript. Below are some common methods:
1. Using the isNaN() method
The isNaN() method is used to check if a value is not a Number. It returns true if the value is NaN (Not-a-Number) and false if the value can be converted into a valid number.
Syntax
isNaN(testingValue);
Now let's understand this with the help of an example:
JavaScript function isNumber(value){ try{ if(isNaN(value)){ throw new Error("Passed value is not a number"); } console.log("Passed value is a number"); } catch(error){ console.log("An error occurred: ", error.message); } } isNumber(55); isNumber("58"); isNumber("GeeksforGeeks"); OutputPassed value is a number Passed value is a number An error occurred: Passed value is not a number
NOTE: The isNaN() method converts the value to a number before checking, which may lead to unexpected results in some cases.
2. Using the typeof operator
The typeof operator can be used to perform the type check of the passed value and compare it with the number type to check whether it is a number or not.
Syntax:
typeof testingValue;
Now let's understand this with the help of example:
JavaScript function isNumber(value){ try{ if(!(typeof value === 'number')){ throw new Error("Passed value is not a number"); } console.log("Passed value is a number"); } catch(error){ console.log("An error occurred: ", error.message); } } isNumber(123); isNumber("123"); isNumber("GFG"); OutputPassed value is a number An error occurred: Passed value is not a number An error occurred: Passed value is not a number
3. Using the Number.isInteger() method
The Number.isInteger() method can also be used to check if a value is number or not. It is mainly used for checking the integer values.
Syntax:
Number.isInteger(testingValue);
Now let's understand this with the help of example:
JavaScript function isNumber(value){ try{ if(!(Number.isInteger(value))){ throw new Error("Passed value is not a number"); } console.log("Passed value is a number"); } catch(error){ console.log("An error occurred: ", error.message); } } isNumber(69); isNumber("231"); isNumber("Geek"); OutputPassed value is a number An error occurred: Passed value is not a number An error occurred: Passed value is not a number
4. Using the Number.isFinite() method
The Number.isFinite() method is used to check if the passed value is finite or not. If it unables to parse the value it returns false and if it parses the value then it check if it is finit or infinite.
Syntax:
Number.isFinite(testingValue);
Now let's understand this with the help of example:
JavaScript function isNumber(value){ try{ if(!(Number.isFinite(value))){ throw new Error("Passed value is not a number"); } console.log("Passed value is a number"); } catch(error){ console.log("An error occurred: ", error.message); } } isNumber(108); isNumber("11"); isNumber("Hello"); OutputPassed value is a number An error occurred: Passed value is not a number An error occurred: Passed value is not a number
Why Checking if a Value is a Number is Important?
In JavaScript, not all values are of the "Number" type, and you might encounter:
- Strings that represent numbers (e.g., "123").
- NaN (Not-a-Number), which is a special value in JavaScript.
- Other data types like objects, arrays, or undefined that may need validation before performing number-specific operations.
Conclusion
In JavaScript, checking if a value is a number is important for tasks like user input validation and calculations. Methods such as isNaN(), typeof, Number.isInteger(), parseInt(), and the unary plus (+) operator help easily determine if a value is a valid number, ensuring smooth data handling and avoiding errors.
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