Apple script find and replace text - applescript

Question

So, right now my code clicks on a textarea in safari then it adds a word using keystroke, however I was wondering if there is a way to find and replace a word in that area and also is there a way to replace a highlighted word without keystroke?
Current code:
Sorry its very very poorly formatted since I am pretty bad at applescript
to clickClassName(theClassName, elementnum)
tell application "Safari"
do JavaScript "document.getElementsByClassName('" & theClassName & "')[" & elementnum & "].click();" in document 1
end tell
end clickClassName
to clickID(theId)
tell application "Safari"
do JavaScript "document.getElementById('" & theId & "').click();" in document 1
end tell
end clickID -- All the code up to this point did is allow me to click on IDs and classes in safari.
tell application "Safari" to activate
tell application "System Events"
tell application "Safari"
tell window 1
set current tab to (make new tab with properties {URL:"https://en.wikipedia.org/w/index.php? title=User:USERNAMEHERE/sandbox&action=edit"})
end tell
end tell
end tell
delay 2 -- All the code up to this point from the last comment did is open a new tab in safari.
repeat 5 times
set randomlist to {"1","2","3","4"} -- List of numbers that will be randomly selected and put in the texarea
set randomword to some item of randomlist
clickClassName("tool-button wikiEditor-toolbar-spritedButton", 0) -- This clicks the bold button on the sandbox page
tell application "System Events"
tell process "Safari"
keystroke randomword -- Uses keystroke to put replace the text inside the bold formatting area
end tell
end tell
delay 1
clickID("wpSave") -- Clicks save
delay 2
tell application "Safari" to set the URL of the front document to "https://en.wikipedia.org/w/index.php? title=User:USERNAMEHERE/sandbox&action=edit" -- Goes back to sandbox and repeats the process
delay 2
end repeat
If you want to test this then put in your wikipedia username in the link and login into your account. Pretty much its a wikipedia bot that will just put stuff in my wikipedia sandbox