The following three language constructs help with debugging. They should obviously be complemented by a proper debugger:
debugger statement behaves like a breakpoint and launches the debugger.
console.log(x) logs the value x to the console of the JavaScript engine.
console.trace() prints a stack trace to the engine’s console.
The console API provides more debugging help and is documented in more detail in The Console API. Exception handling is explained in Chapter 14.