Google reCaptcha 2 JavaScript Validation (client side)
reCaptcha is a great “bot” detection solution from Google. Google watches the pattern of user interaction to decide whether it is a “bot” or a real user. It is near impossible for a “bot” to simulate those patterns. So reCaptcha succeeds in blocking spam most of the time. Versions of reCaptcha reCaptcha version 1 reCaptcha version 1 used to show a couple of words in an image and the user had to enter the words in a box to prove they are not “bots”.