In this tutorial, I am going to show you how to check if a string is a number or not in JavaScript.
To check if a string is a number in JavaScript, there are several methods you can use, each with its own advantages. In this article, i am going to mention 4 different methods with examples to detect if a string is a number.
1. Using isNaN and parseFloat/parseInt
The first method involves parsing the string as a floating-point number (or an integer) and then checking if the result is NaN (Not a Number). If the value is Nan, that means it must be a number.
function isNumber(str) {
return !isNaN(parseFloat(str)) && isFinite(str);
}
2. Using Regular Expression
The following method using regular expressions to check if a string strictly represents a number. Regular expressions can be tailored to your specific requirements (like allowing decimals or not).
function isNumber(str) {
return /^[0-9]+(\.[0-9]+)?$/.test(str);
}
This regex checks for integers or decimal numbers. You can adjust the regex based on what you consider a valid number (e.g., including/excluding negatives, scientific notation, etc.).
3. With Number.isFinite
In this example, we are converting the string to a number using the Number constructor and then checking if it is a finite number.
function isNumber(str) {
return Number.isFinite(Number(str));
}
4. Using + Unary Operator
The unary + operator attempts to convert the string to a number. Then you can check if the result is finite.
function isNumber(str) {
return Number.isFinite(+str);
}
Each of these methods discussed above has different behaviors, especially when dealing with edge cases like strings containing only whitespace, special numeric values (like Infinity), or non-standard numeric formats. Choose the method that best fits for you.