Javascript function for validating numbers

Inside the function, the arguments (the parameters) behave as local variables. If the function was invoked from a statement, Java Script will "return" to execute the code after the invoking statement. The return value is "returned" back to the "caller": Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.

Local variables are created when a function starts, and deleted when the function is completed.

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.

The purpose of a form validation script is to return a boolean value ( to reference form fields, but that can lead to namespace conflicts and why make things more complicated than necessary.

When the form is submitted - either by hitting Enter or clicking on the Submit button - the to abort (cancel) the form submission. In a real-life situation you will most likely have more fields to check, and more complicated conditions, but the principle remains the same.

Validating form input with Java Script is easy to do and can save a lot of unnecessary calls to the server.

Otherwise a browser with Java Script disabled, or a hacker trying to compromise your site, can easily by-pass client-side validation.

For an alternative approach to client-side form validation, without Java Script, check out our new article on HTML5 Form Validation which is available now in most modern browsers. The first test in the example is therefore only necessary in order to provide a different error message when the input is blank.

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.

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