Hailey Bieber, Kendall Jenner All Smiles at Justin Bieber's Album Release Party

Justin Bieber's album release attendees have all the "SWAG" in the world ... with some of the biggest celebs in Hollywood pulling up to the big event Thursday night.

Of course, Justin and his wife Hailey were front and center at The Bird Streets Club in West Hollywood ... spotted holding hands. And, from the expression on Hailey's face later on, it looks like she had an incredible night!

JB brought his eclectic aesthetic to the party ... pink hoodie, white beanie and bright green socks -- with pants sagging so low they're basically sliding off.

Kendall Jenner proved classic black can never be replaced in a sleeveless top and tight leggings. She's holding hands with a dude here and covering part of her face with her hands ... probably do to all the lights being on her -- as per usual.

Kendall and her mystery guy are laughing together ... and, he's holding what appears to be a bottle of Don Julio 1942 for the two to sip on while they're out on the sidewalk.

She was also photographed in close quarters with another dude while riding in a van later on.

The Kid LAROI went with a casual-chic outfit ... button-down white shirt and black slacks -- hopping down from the van he shared with a group before Bieber made his presence felt.