Check if a String is a Valid Number in JavaScript

General Discussions
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1

How can I check if a string is a valid number in JavaScript, similar to the IsNumeric() function in VB6?

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2

With my experience, a simple and quick method is using JavaScript’s built-in isNaN() function to check if a string is a valid number. Essentially, if isNaN() returns false, it indicates the string is a valid number in JavaScript."_

function isValidNumber(str) {
    return !isNaN(str);
}

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

This approach gives a straightforward way to check if a string is a number in JavaScript without diving into more complex logic.

3

I’ve found another effective approach is to use parseFloat() or parseInt(). With these functions, you can attempt to convert the string and then double-check if the result is a valid number with isNaN() and isFinite()."_

function isValidNumber(str) {
    const num = parseFloat(str);
    return !isNaN(num) && isFinite(num);
}

console.log(isValidNumber("123.45"));  // true
console.log(isValidNumber("abc"));     // false

In this method, the parsing functions add an extra layer by trying to convert the string first. This helps when you want to check if a string is a number in JavaScript, especially when dealing with decimals.

4

For cases where you need more precise control, you might consider using a regular expression. In my experience, regex gives you the ability to directly match a valid number format."_

function isValidNumber(str) {
    const regex = /^-?\d+(\.\d+)?$/;
    return regex.test(str);
}

console.log(isValidNumber("123"));      // true
console.log(isValidNumber("12.34"));    // true
console.log(isValidNumber("abc"));      // false

This regex approach is ideal if you need to account for more specific patterns like allowing negative numbers. It’s a great way to check if a string is a number in JavaScript using clear rules.