keyword, followed by a name, followed by parentheses ().
Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).
In more complicated forms you will want to set conditions on the form that combine multiple elements.
For example, a text input that only needs to have a value if a checkbox is checked: Using simple logical operators and the functions supplied above you can do all sorts of client-side form validation.
This is done using HTML5 form validation techniques and CSS, but it only validates the input format (pattern) and not the actual values.
That could be done using Ajax, but would make the CAPTCHA much easier to break.
But if the user unchecks the box, the user DOESNT have to enter info in textarea.
However, it turns out that The is Na N() function determines whether a value is an illegal number (Not-a-Number).
Just set the Character length( Maximum and minimum) of the field, please see the attached Screenshot for reference.
Validating form input with Java Script is easy to do and can save a lot of unnecessary calls to the server.
To take things a step further you can even explore Ajax Form Validation which lets you supply real-time feedback using server-side scripts triggered by Java Script events.
The team at have made a video based on this article as a part of their Java Script training lessons which you can view below. Would be great if you could post full examples of code including form and not just pieces that fit into the greater framework of code.