Extroverts often:
- Have high energy
- Talk more than listen
- Think out loud
- Act, then think
- Like to be around people a lot
- Prefer a public role
- Can sometimes be easily distracted
- Prefer to do lots of things at once
- Are outgoing & enthusiastic

Introverts often:
- Have quiet energy
- Listen more than talk
- Think quietly inside their heads
- Think, then act
- Feel comfortable being alone
- Prefer to work "behind-the-scenes"
- Have good powers of concentration
- Prefer to focus on one thing at a time
- Are self-contained and reserved

But I think she can be extrovert too.

Definitely!

She keeps to herself, and she actually thinks before she does. I don't see her being as open as the other princesses.

Her only friend is Raja

I'm surprised so many people think she's an introvert. I'd definitely say she talks more than listens, acts before thinking, she is quick to make friends with Aladdin. Sure, her only friend is Rajah, but she had no chance to make other friends.

^ Exactly, you can't really judge her in terms of extrovert/introvert based on her situation because the situation is out of her hands (at the beginning of the movie, anyway).
Jasmine does act slightly introverted at times in the movie, but I think she's an extrovert at heart, while having aspects of both IMO.

She's quite both.

She voices her opinion, I think it's pretty clear.

she's outspoken, self-confident, full of energy, acts then thinks, etc. she isn't the Super Extrovert Ariel is but it's there.