In terms of syntax, template expressions are similar to JavaScript. Many JavaScript expressions are legal template expressions, with a few exceptions.

You can't use JavaScript expressions that have or promote side effects, including:

Assignments (=, +=, -=, ...)
Operators such as new, typeof, instanceof, etc.
Chaining expressions with ; or ,
The increment and decrement operators ++ and --
Some of the ES2015+ operators
Other notable differences from JavaScript syntax include:

No support for the bitwise operators such as | and &
New template expression operators, such as |, ?. and !