(Built-in) way in JavaScript to check if a string is a valid number

Question

I\'m hoping there\'s something in the same conceptual space as the old VB6 IsNumeric() function?

Answer 1

If you're just trying to check if a string is a whole number (no decimal places), regex is a good way to go. Other methods such as isNaN are too complicated for something so simple.

    function isNumeric(value) {
        return /^-?\d+$/.test(value);
    }
    
    console.log(isNumeric('abcd'));         // false
    console.log(isNumeric('123a'));         // false
    console.log(isNumeric('1'));            // true
    console.log(isNumeric('1234567890'));   // true
    console.log(isNumeric('-23'));          // true
    console.log(isNumeric(1234));           // true
    console.log(isNumeric('123.4'));        // false
    console.log(isNumeric(''));             // false
    console.log(isNumeric(undefined));      // false
    console.log(isNumeric(null));           // false

To only allow positive whole numbers use this:

    function isNumeric(value) {
        return /^\d+$/.test(value);
    }

    console.log(isNumeric('123'));          // true
    console.log(isNumeric('-23'));          // false