Pop up when field not filled

[Dan27265774kig3]

I'd like to have a pop up appear if users click a specific field and then leave it blank. Field is called "Location." The pop up should say something like "This information is required to process this referral." Is there any way to do this using javascript?

Unfortunately I know nothing about javascript.

[JR Boulay]

Place this in the "on blur" trigger:

if (event.target.value == event.target.defaultValue) {app.alert("This information is required to process this referral.");}