屏蔽输入文字，仅输入4位数字

Question

I am trying restrict a user from entering more than 4 digits.

For that I am using:

$("#YEAR").mask("(9999)");

But I'm getting the following error:

JavaScript runtime error: Object doesn't support property or method 'mask'

Do I need to include a library for it?

Answer 1

A simple solution could be:

 $(function () { $('#YEAR').on('keypress', function(e) { var charCode = (e.which) ? e.which : event.keyCode if (charCode < 48 || charCode > 57) { return false; } return true; }) }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <form> <input type="text" maxlength="4" id="YEAR" name="YEAR"/> </form>