Javascript not working in body field. Using Full HTML
Most likely , your FULL HTML content authoring text format settings are limiting the markup you can use, stripping out the script (that's default behavior).

You can either:
1. Modify the settings for the text format to not restrict markup
2. Create a new text format, without any of the filter options enabled; then switch the format on the body field in which you want to insert the script. 

If these options still fail, you may have a theme where a preprocess hook or twig filter is stripping out the script.