TikTok's videos are goofy. Its strategy to dominate social media is serious

China's first big hit in the US uses an advanced algorithm to personalise its video-sharing app, and parent Bytedance's enormous ad spending on Snap, Facebook and Instagram aims to hook their users

Sometime in 2018, executives at Snap Inc. realized their biggest advertiser was also a rising competitor. It was an addictive app featuring cat videos, pranks and people doing robot dances. The Chinese video-sharing app TikTok was splurging by spending nearly $1 billion on advertising for the year, according to a person familiar with the spending, helping turn it into the first ever Chinese consumer-tech company to break out big in the U.S.

TikTok has also flooded Facebook Inc. and Instagram with ads, rattling the social-media giants by targeting their audiences on their own turf.

Its Beijing-based parent, Bytedance Inc., is now among