If textarea conatins "eat" then output a line of text saying "something"

I am currently writing a text adventure (web-based) and I need a textarea which the player can write in, and if this textarea contains a certain word (e.g. eat) the next line of code should appear. Enter has the function of submitting the message. -> If the submitted message is "eat" output "something".

Since english is not my native language, please ignore mistakes.