Javascript：如何从键入的表单中找到类似的短语或文本？

Im just practicing with new code and iv got stuck. I want to be able to open a form to post a question on my site, however I was it to show questions that have already been asked which could be similar to what they are asking. So basically like on this site, While im writing this question it shows "Questions that may already have your answer". That is what I want, but cant find how to do it. So I want to be able to write in the form and some code searches questions already in the database to find similar questions. Does anyone know how to do this?Im just practicing with new code and iv got stu