Question

I am trying to check that what the user inputs begins with two letters, followed by either 6, 8 or 10 numbers. Checking string length should be ok but is there a neater way to check that the first two characters are letters and that the subsequent 6, 8 or 10 characters are numbers than converting each character to unicode and then checking that way?

Answer 1

You can use regex:

^[a-zA-Z]{2}(?:\d{6}|\d{8}|\d{10})$

This will pass only if the first 2 are alphas and next 6 or 8 or 10 are numbers.

JS:

function isValid(txt) {
    return /^[a-zA-Z]{2}(?:\d{6}|\d{8}|\d{10})$/.test(txt);
}

alert(isValid("ab123456"));   // pass
alert(isValid("ab1234567"));  // fail, contains 7 digits
alert(isValid("abc123456"));  // fail, starts with 3 chars 
alert(isValid("ab12345678")); // pass

Here’s complete JS example: http://jsfiddle.net/mrchief/sRLrW/