A lot of problems may come from syntax. You aren't necessarily guaranteed the type of a variable when passing a variable to a function. Variables can be any type and compared to other languages such as Java and C++, it may be a bit more confusing.

There also may be some confusing syntactical things such as checking for equality with ===. Given that though, it is a very useful language for something written in 10 days.

JavaScript: Designing a Language in 10 Days