To set a value in CKEditor with JavaScript, we use the setData method.
For instance, we write
CKEDITOR.instances["fieldName"].setData("your data");
to get the CKEditor instance with CKEDITOR.instances["fieldName"].
Then we call setData with "your data" to set the field’s value to "your data".
Conclusion
To set a value in CKEditor with JavaScript, we use the setData method.