This is very common from what I've observed. The more experience you get, the more you learn, the more there is to do, the less you will care about remembering every last bit of syntax 100% of the time ;)
Most embarrassing story: under live-coding interview stress, I was trying to update an attribute and forgot the name of jQuery's .attr(). Very embarrassing! I got the job though. A related take-away is that a job interview is a really bad place to pair program for the first time in your life.