How can I explain this. I have a list of postcodes in text files in an external url and I have a formfield.

When people enter data into the form field, using javascript validation, I want the form to check if the entered data exists in any of the external postcode files.

Is there anyway this can be possible ? if so can you please explain.

Thanks in advance.

This may be possible. What have you tried? Please demonstrate some effort!

I have over 2 million UK postcodes in multiple flat files and I have a static search field.

When people enter data into the search field, I want the field to guess or autocomplete the field based on the data input.

So when a visitor is entering their postcode in the field, I don't know how to make it happen that the fields prediction or autocomplete is fetched from the multiple postcode flat files.

I have thought of using a simple dropdown list, but that would be a very long list as you can imagin.

I really need help with this.

you wouldn't be able to do this with plain js you'd need to use ajax and return a json list of possible values from your external file(s)

thousands in flat files sounds like a terrible idea, you might want to consider a database