WordPress by default used Visual editor as the base of all its editor, such as the page/post editor and the “Text” widget editor (with the latest version 4.8 update). Here are how you can change it to Text editor.

Sometimes you would need to use a Text editor to insert, for example a series of Javascript/tracking code on the certain page and/or post. Or you need to insert a Javascript banner advertisement code in “Text” widget. Here are how to:

Page/Post Editor

 

“Text” Widget Editor