No, I'm talking for the Default Value which anyone can enter in Textarea or WYSIWYG Editor fields.
For example in the site form view I created a WYSIWYG Editor field, and in its configuration there is a Default Value button which opens a box where I can enter some text as the default value and it shows in the text area in the front end when rendered. So, my question is how do we enter the value of already existing field together with the text.
I don't want to get the default value of a field. I need to get the value of a field as the default value for a text area or WYSIWYG editor.
For example, lets say I have a text field which has a value of 555. I need to pre populate the text area field with the value of the text field - 555. We can enter static text in the textarea field by setting the Default Value option of the teaxtarea field, but I need the text to be dynamic.
Seems I misunderstood your question :) You can solve this by using
conditionals, put isFilledBy conditional on text area with isFilled
condition. Another way would be to us SD live field, but that field is
no longer maintained (currently you just need to change one class name
to make it work, search this forum for details).