How to Validate Decimal Number in JavaScript

While working with web development, there may be situations where we need to parse a string/number and verify if it is a decimal number or not. In this article, we will learn how to validate decimal number in JavaScript.

How to Validate Decimal Number in JavaScript

By default, most developers use isNumeric() function to determine if a string/number is decimal number or not.

isNumeric(n)

But isNumeric() function fails in many use cases as shown below.

// Whitespace strings:
IsNumeric(' ')    == true;
IsNumeric('\t\t') == true;
IsNumeric('\n\r') == true;

// Number literals:
IsNumeric(-1)  == false;
IsNumeric(0)   == false;
IsNumeric(1.3) == false;
IsNumeric(9e5) == false;

So we need to make use of two JS functions for this purpose isNaN(), parseFloat() and isFinite(). parseFloat() parses an argument and returns a floating point number. isNaN() checks if a given value is NAN (Not a Number), which can be the result of parseFloat() in case the input is not a number. We also use isFinite() function to determine if it is not infinite. Combining these you can check if a number n is decimal or not as shown below.

return !isNaN(parseFloat(n)) && isFinite(n);

You can create your own isNumeric() function incorporating the above expression.

function isNumeric(n) {
    return !isNaN(parseFloat(n)) && isFinite(n);
}
//e.g isNumeric(4.5) returns true

In this article, we have learnt how to validate decimal number in JavaScript. It can be used for data validation in your website or web applications.

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