Javascript try…catch…else…finally like Python, Java, Ruby, etc

Question

How can Javascript duplicate the four-part try-catch-else-finally execution model that other languages support?

A

Answer 1

Javascript does not have the syntax to support the no-exception scenario. The best workaround is nested try statements, similar to the "legacy" technique from PEP 341

// A pretty-good try/catch/else/finally implementation.
try {
  var success = true;
  try {
    protected_code();
  } catch(e) {
    success = false;
    handler_code({"exception_was": e});
  }
  if(success) {
    else_code();
  }
} finally {
  this_always_runs();
}

Besides readability, the only problem is the success variable. If protected_code sets window.success = false, this will not work. A less readable but safer way uses a function namespace:

// A try/catch/else/finally implementation without changing variable bindings.
try {
  (function() {
    var success = true;
    try {
      protected_code();
    } catch(e) {
      success = false;
      handler_code({"exception_was": e});
    }
    if(success) {
      else_code();
    }
  })();
} finally {
  this_always_runs();
}