Quickjs doesn't print user-defined exceptions with their toString()

[ivankra]

User-defined exceptions are dumped as a plain json object without calling their toString() - this can lose valuable bits of information. For test262 purposes, for example, class name information is lost:

$ cat exc.js 
function Test262Error(message) {
  this.message = message || "";
}
Test262Error.prototype.toString = function () {
  return "Test262Error: " + this.message;
};
throw new Test262Error("foo");
$ ./qjs exc.js
{ message: "foo" }

In contrast, for standard exceptions:

$ ./qjs -e 'throw new RangeError("foo");'
RangeError: foo
    at <eval> (<cmdline>:1:21)

quickjs-ng gets it right.

js_std_dump_error1 should switch from JS_PrintValue to JS_ToCString.

A stack trace would be nice too, but probably more work.