验证在输入字段中不是实时的

i want to make prefix validation on my site, I have been looking for and get what I want, but the problem is, when I was type a value in the input form does not issue notice an error or not, when I click in any place that focus is not in the input field error notice to appear. I want when I am typing in the input field and it appears immediately notice one of them without having to click anywhere in advance. if anyone could help me?i want to make prefix validation on my site, I