Change Value Of An Item If A Class Of Another Changes

I have a drop down menu with a few options of delivery method. One option is "other" and when a user selects other a new text box appears for them to specify. this is using javascript to change the css class of the div containing textbox. all this works fine and user can change between options resulting in textbox appearing when selected other and disappearing when selecting anything else. however if the user selects other and enters text into textbox then chages their mind and selects a new option the textbox will disappear but the value that was entered remains the same, i need to default when textbox is hidden to reset value.