Check if String is Number in JavaScript [10 Methods]

Olorunfemi Akinlua


Welcome to this detailed tutorial where we will unravel various methods to check if string is number in JavaScript. In programming and web development, it’s often essential to validate the data we work with. Ensuring that the data is of the correct type is crucial for the accuracy and reliability of our applications. In JavaScript, a language known for its flexibility and dynamism, checking the type of data, especially whether a string is a number, is a common yet critical task.

In this tutorial, we are going to explore a multitude of ways to perform this check, ensuring you have a comprehensive set of tools at your disposal. We will start by understanding the basics of strings and numbers in JavaScript, diving into the significance of validating strings as numbers.

Moving forward, we will delve into manual methods of validation, such as using Regular Expressions and iterating through characters. We will also discuss built-in JavaScript methods like isNaN(), and modern ES6+ methods such as Number.isNaN() and Number.isInteger() for efficient and reliable checks.

In addition to these, we will touch upon leveraging popular JavaScript libraries for this purpose and go through special cases and considerations that often come up in real-world scenarios. We’ll wrap it up by sharing best practices, error handling techniques, and practical applications of these methods in various use-cases.


Manual Methods to Check if String is Number

When you need to check if a string is number in JavaScript, various manual methods can be utilized. These methods do not rely on built-in JavaScript functions but use fundamental programming concepts and logic to perform the validation. Let’s delve deep into these methods.


1. Using Regular Expressions

Regular expressions (regex) are a powerful tool in JavaScript, allowing us to match patterns in strings. We can craft a regex pattern to identify whether a string strictly consists of numeric characters, hence allowing us to check if string is number.

Description: A regular expression can be constructed to match strings that represent numbers, including handling cases like negative numbers and decimals. By using the test() method with the appropriate regex pattern, we can verify the numeric nature of a string.

function isNumeric(str) {
  const pattern = /^-?\d+(\.\d+)?$/; 
  return pattern.test(str);

console.log(isNumeric("123")); // true
console.log(isNumeric("-123.45")); // true
console.log(isNumeric("abc")); // false


2. Iterating through each character

Another method to "check if string is number in JavaScript" is by iterating through each character in the string and verifying whether each character is a digit.

Description: In this approach, a loop is used to go through each character of the string. We then ascertain whether each character is within the range of numeric characters (0-9). Additional checks can be added to handle cases like decimals and negative numbers.

function isNumeric(str) {
  for(let i = 0; i < str.length; i++) {
    if(str[i] < '0' || str[i] > '9') {
      return false;
  return true;

console.log(isNumeric("123")); // true
console.log(isNumeric("123a")); // false


3. Checking against ASCII values

ASCII values can also be utilized to check if string is number in JavaScript. Each character, including digits, has a corresponding ASCII value, and this can be used for validation.

Description: In this method, we use the ASCII values of characters to verify if they are numeric. The ASCII values of digits 0-9 lie between 48 and 57. We can leverage this by comparing the ASCII values to check the numeric nature of the string.

function isNumeric(str) {
  for(let i = 0; i < str.length; i++) {
    const ascii = str.charCodeAt(i);
    if(ascii < 48 || ascii > 57) {
      return false;
  return true;

console.log(isNumeric("123")); // true
console.log(isNumeric("1a3")); // false


Using JavaScript Built-in Methods

JavaScript comes equipped with several built-in methods that facilitate the task to check if a string is number in JavaScript. These methods are ingrained within the JavaScript language, providing a straightforward way to validate strings as numbers. Let’s explore these methods in detail.


1. isNaN() Function

The isNaN() function is used to determine whether a value is NaN (Not-a-Number). It’s a handy function when you want to verify if a string can be converted to a valid number.

Description: When a string is passed to the isNaN() function, it tries to convert the string into a number. If the conversion is not successful, it returns true, indicating that the string is not a number.

console.log(isNaN("123")); // false
console.log(isNaN("abc")); // true
console.log(isNaN("123abc")); // true


2. Number() Function

The Number() function can convert a string into a number. It is useful to check if string is number in JavaScript as it returns NaN if the string can't be converted.

Description: Passing a string to the Number() function attempts to convert the string into a numeric value. If the conversion is successful, it returns the numeric value; otherwise, it returns NaN.

console.log(Number("123")); // 123
console.log(Number("abc")); // NaN
console.log(Number("123abc")); // NaN


3. parseInt() and parseFloat() Functions

The parseInt() and parseFloat() functions parse a string and return an integer or a floating-point number, respectively.

Description: These functions parse the string from left to right until a character that is not a valid digit is encountered. parseInt() returns an integer, while parseFloat() returns a floating-point number. To strictly check if string is number in JavaScript, you might want to ensure that the entire string is considered in the conversion.

console.log(parseInt("123")); // 123
console.log(parseInt("123abc")); // 123
console.log(parseFloat("123.45")); // 123.45
console.log(parseFloat("123.45abc")); // 123.45


Leveraging JavaScript Libraries

Utilizing JavaScript libraries such as Lodash and jQuery can be quite beneficial when you need to check if string is number in JavaScript. These libraries come with a variety of utility functions that can simplify the validation process.


1. Using Lodash

Lodash is a powerful utility library that comes with various functions to manage and manipulate data.

Description: Lodash has a function called _.isNumber(), which can be used to verify if a value is a number. However, since it doesn’t directly operate on strings, additional steps are required to perform the validation on a string.

const _ = require('lodash');

function isNumeric(str) {
  const number = Number(str);
  return _.isNumber(number) && !isNaN(number);

console.log(isNumeric("123")); // true
console.log(isNumeric("abc")); // false


2. Using jQuery

jQuery, primarily known for DOM manipulation, doesn’t have a dedicated function to check numeric strings. However, you can leverage its ability to work with JavaScript seamlessly.

Description: You can use jQuery in combination with the native JavaScript methods to check if string is number in JavaScript. jQuery's role here would be more about enhancing the user experience, such as collecting input from form fields.

// Assuming you have jQuery loaded
function isNumeric(str) {
  return !isNaN(Number(str));

// Usage with jQuery to get value from an input field
const value = $("#inputField").val();
console.log(isNumeric(value)); // Output depends on the input value


Modern ES6+ Methods

Modern JavaScript (ES6 and beyond) provides refined methods to check if string is number in JavaScript, making the validation process more precise and reliable.


1. Number.isNaN()

This method is a more robust version of the global isNaN() function and is used to determine whether a value is NaN.

Description: Number.isNaN() is a reliable method to check if a value is NaN as it doesn’t coerce non-number types into numbers, providing a more accurate result.

console.log(Number.isNaN(NaN)); // true
console.log(Number.isNaN(Number("abc"))); // true
console.log(Number.isNaN("abc")); // false


2. Number.isInteger()

The Number.isInteger() method determines whether a value is an integer.

Description: This method can be used to check if a string is number in JavaScript by verifying if the converted number value of a string is an integer.

console.log(Number.isInteger(Number("123"))); // true
console.log(Number.isInteger(Number("123.45"))); // false
console.log(Number.isInteger(Number("abc"))); // false


Frequently Asked Questions (FAQs)

What is the best method to check if string is number in JavaScript?

The "best" method depends on the specific requirements of your task. For simple validations, using built-in JavaScript methods like isNaN() or Number() is quite effective and straightforward. If you need to handle more complex scenarios, such as considering whitespaces, decimals, or scientific notation, you might want to use regular expressions or iterate through each character for a custom validation.

Can I use the typeof operator to check if string is number in JavaScript?

No, the typeof operator won’t be effective to directly check if a string is numeric. The typeof operator will return "string" for any string value, regardless of its content. However, you can first convert the string to a number and then use typeof to check if the conversion was successful, but there are more straightforward methods like isNaN() or Number().

Why might the isNaN() function not always be reliable for this validation?

The isNaN() function can sometimes give unexpected results because it coerces the value passed to it into a number. For example, isNaN(' ') will return false because a space is coerced to zero (0), which is a number. Therefore, using Number.isNaN(Number(value)) or other validation methods might be more reliable for strictly checking if string is numeric value.

What considerations should be made for strings representing floating-point numbers?

If a string represents a floating-point number and you want to validate it, consider methods that accommodate decimal points. Regular expressions, parseFloat(), and the Number() function are suitable for handling such scenarios, as they can correctly interpret and validate strings with decimal points as numeric values.

How to handle strings representing numbers in scientific notation?

If you are dealing with strings that may contain numbers in scientific notation (e.g., "1e5"), you might want to use methods like the Number() function or a well-crafted regular expression. These approaches can correctly interpret and validate such strings as numeric values, ensuring that scientific notation is appropriately handled in the validation process.

Is it necessary to consider negative numbers during the validation?

Yes, if your use case allows for negative numbers, your validation logic should account for the possibility of a leading minus sign (-) in the string. Various methods, such as regular expressions or a combination of manual validations and built-in functions, can be used to ensure that negative numbers are validated correctly.



Throughout this tutorial, a multitude of methods to check if string is number in JavaScript has been meticulously explored and elaborated upon. Here’s a brief recap:

  • Manual Methods for Validation: Including the use of regular expressions, iterating through each character, and checking against ASCII values.
  • Using JavaScript Built-in Methods: Such as isNaN(), Number(), parseInt(), and parseFloat().
  • Leveraging JavaScript Libraries: Utilizing libraries like Lodash and jQuery to facilitate the validation process.
  • Modern ES6+ Methods: Incorporating modern ES6+ methods such as Number.isNaN() and Number.isInteger() for more reliable and straightforward validations.

Each method carries its own set of advantages, allowing for flexibility based on the specific requirements of your validation task. Whether it's the simplicity of built-in methods, the precision of manual approaches, or the enhanced functionalities offered by libraries and modern ES6+ methods, choosing the right strategy will be instrumental in effectively validating numeric strings in JavaScript.


Further Reading Resources


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Olorunfemi Akinlua

He is boasting over five years of experience in JavaScript, specializing in technical content writing and UX design. With a keen focus on programming languages, he crafts compelling content and designs user-friendly interfaces to enhance digital experiences across various domains. You can connect with him on LinkedIn.

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