Checking if the first character of a string is a number gives an error that charat is not a valid method

Question

I have a method that validates a field against 3 regex expressions and returns an error based on which expression failed.

function mfpValidateValue()
{
    var pCtrl = window.document.forms[0].txtValue;

    var pStrValue  =  mTrim(pCtrl.value);
    if (pStrValue == '')
        return true;

    var regexNum = new RegExp("^[0-9]{9}.{0,3}$"); // First 9 are numeric followed by up to any 3 characters
    var regexLetter1 = new RegExp("^[A-Z]{1,3}[0-9]{6}$"); //Up to the first 3 are alpha, then there are exactly 6 numbers
    var regexLetter2 = new RegExp("^[A-Z]{1,3}[0-9]{9}$"); //Up to the first 3 are alpha, then there are exactly 9 numbers
    var error = "";

    // If any of the RegEx fails, set base error message
    if (!regexNum.test(pStrValue) || !regexLetter1.test(pStrValue) || !regexLetter2.test(pStrValue))
        error = "Please enter a valid Value.";

    // Set more specific error message. 
    if (!isNaN(pStrValue.charat(0)))
        error += " If the first character of Value is a digit, then the first nine characters must be digits.";
    else
        error += " If the first character of Value is a letter, up to the first three characters must be letters proceeded by 6 or 9 digits.";

    return (error == "");
}

I get the following error message on this line:

    if (!isNaN(pStrValue.charat(0)))

Object doesn't support property or method 'charat'

And the value in pStrValue is:

"12345678"

Is JavaScript using the term "object" ambiguously here to refer to my particular variable, or does it actually think pStrValue is an object and not a string?

Answer 1

You check this:

if not is Not a Number

The new ECMAScript 2015 (ES6) has a new method:

Number.isInteger(value)

Mozilla Developer Network describes:

If the target value is an integer, return true, otherwise return false. If the value is NaN or infinite, return false.

See full information: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger

A proper alternative is:

if (Number.isInteger(parseInt(pStrValue.charAt(0))))