Basic Troubleshooting

Step 1:
View your site using Chrome or Firefox: If you have Chrome, right click on the page and select “inspect element.” Then click on the “console” tab. This will show you any Javascript errors that your site may be experiencing. If you have Firefox, you’ll need to download the FireBug extension, then go to the error console. If there is an error, it will include a filename and line number. If the filename is within a plugin, try deactivating that plugin and reload the page. This first step is very important, so don’t overlook it.

Step 2:
View the source of your page: Using any browser, right click on your page and select “view source.” With the source opened, use the search feature of your browser (often CTRL + F) to search for ‘jQuery’ without the single quotes. Paging through the results, look for multiple instances of jQuery.js, jQuery.1.3.4.js, jQuery.1.8.2.min.js, or something similar. Keep in mind that a lot of jQuery extensions are named jQuery.somethingCool.js. To quote Obi-Wan, those aren’t the ones you’re looking for. If you locate multiple inclusions of jQuery, you have probably uncovered the cause of your Javascript woes. To find out where the multiple calls are coming from, you’ll need to change your theme over to the basic “twenty twelve” WordPress theme, and deactivate plugins one by one. Once you find the culprit, feel free to email their creators asking them to fix their poor coding choices.

Step 3:
Switch to a default WordPress Theme such as Twenty-Seventeen: I mentioned this in the previous step, but it bears repeating: if you have jQuery or Javascript errors on your page, revert back to a basic WordPress Theme. This is especially true if you have purchased a third party theme or had a theme developed by someone else. Theme authors are notorious for improperly adding their own Javascript and/or jQuery.

Step 4:
Deactivate all of your plugins: In order to find which plugin is causing your Javascript issues, you’ll have to do a bit of leg-work. I know that it sucks to deactivate and reactivate 20 plugins, but there’s just no way around it. Once all of your plugins are deactivated, activate them one at a time, reloading the page between each activation. Once the Javascript on your page stops working properly, you have probably found the problem plugin. I say probably because it is possible that there are multiple plugins improperly using Javascript or jQuery. If you think that you’ve found the problem plugin, deactivate it and go through the rest of your plugins anyway. Hopefully you don’t find any more, but it’s better to be safe than sorry.

Other Things to Check:
Are you on the latest version if WordPress?
Are you on the latest version of Ninja Forms? Ninja Forms is updated frequently with bug patches, security updates, code improvements, and new features. It’s always best to be on the latest version of Ninja Forms.
Are you on the latest version of your Ninja Forms Extensions? Extensions are updated with new features, bug fixes, and to ensure compatibility with the newest version of Ninja Forms core plugin. And old version of Ninja Forms or extensions can definitely cause unintended results. You can check your particular extensions to see if you are on the latest version.