输入框验证

Question

I want to create a Input Box for entering the private entering details of a person, On which first character has to be A or E and rest can be alphanumeric and no special character are allowed. I need to do validation for the same that no one enter any special character and First character has to be A or E (all has to be check on the client side)

Can any one guide me how to proceed

Answer 1

Look in to regex with JavaScript, along with the keydown event. You can attach a function to the keydown event, and inside this function check the input box(es) match and then proceed as you wish.

Something like this: (not tested)

<script>
function checkInput() {
  var inputToCheck = document.getElementById('my_input');
  if (!inputToCheck.value.match(/[AE]\w+/)) {
    // do something here, like alert them or remove special characters with .replace
  }
}
</script>

<input id="my_input" onkeydown="checkInput();" />

Answer 2

If this is the only field to validate I would write my own with js & regexp as Leonard Challis wrote (but on the keyup event).

If there will be a lot of fields and perhaps multiple forms on the site, I would consider a framework. This is pretty good: http://bassistance.de/jquery-plugins/jquery-plugin-validation/

If you would be using that one you could write a custom function for your special needs. http://docs.jquery.com/Plugins/Validation/Validator/addMethod#namemethodmessage

Answer 3

This sounds like a homework assignment (since starting with specifically “E” or “A” sounds very artificial), so I'd suggest first deciding on the interpretation of the task. Should “E” and “A” be interpreted case-insensitively? What exactly does “alphanumeric” mean? For example, is “Σ” or “Я” or “١” alphanumeric? If the purpose is to do the checks client-side, should you try to make the page completely non-functional when JavaScript is disabled, or should you just do the checks client-side as far as possible ? (In the latter case, consider using the pattern attribute in HTML. On some modern browsers, it causes the check to be performed even when JavaScript is disabled.)