Implementing scripts in the Html field is disabled by default. Today we use a variety of Content Filters which you can see here:
As you can see, in your case you will have to disable is the RemoveScripts filter.
First you will have to map your editor template ( you need to map a custom template over default one ) in Sitefinity and then specify which Content Filters should be enabled. Create your editor template and register it in Sitefinity by going to Settings > Advanced > Controls > ViewMap > Telerik.Sitefinity.Modules.GenericContent.Web.UI.ContentBlockDesigner. In LayoutTemplatePath field enter the path to your template( ~/Templates/Editor.ascx ).
Please refer to this forum thread where my colleague Boyan gave some more information about the way you can achieve that ( in addition to this answer here ).
You can paste the following code between <div>, </div> tags of your editor .ascx file:
<%--replace with needed filters--%>
with the names of those filters you want to include in your project.
Also if you want to have flawless working code use Script Widgets ( Java Script ) instead of Content Block for your scripts.
the Telerik team
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