v8/test/mjsunit/error-constructors.js

// Copyright 2011 the V8 project authors. All rights reserved.
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// modification, are permitted provided that the following conditions are
// met:
//
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// Check that message and name are not enumerable on Error objects.
var desc = Object.getOwnPropertyDescriptor(Error.prototype, 'name');
assertFalse(desc['enumerable']);
desc = Object.getOwnPropertyDescriptor(Error.prototype, 'message');
assertFalse(desc['enumerable']);

var e = new Error("foobar");
desc = Object.getOwnPropertyDescriptor(e, 'message');
assertFalse(desc['enumerable']);
desc = Object.getOwnPropertyDescriptor(e, 'stack');
assertFalse(desc['enumerable']);

var e = new Error();
assertFalse(e.hasOwnProperty('message'));

// name is not tested above, but in addition we should have no enumerable
// properties, so we simply assert that.
for (var v in e) {
  assertUnreachable();
}

// Check that error construction does not call setters for the
// properties on error objects in prototypes.
function fail() { assertUnreachable(); };
ReferenceError.prototype.__defineSetter__('name', fail);
ReferenceError.prototype.__defineSetter__('message', fail);
ReferenceError.prototype.__defineSetter__('stack', fail);

var e = new ReferenceError();
assertTrue(e.hasOwnProperty('stack'));

var e = new ReferenceError('123');
assertTrue(e.hasOwnProperty('message'));
assertTrue(e.hasOwnProperty('stack'));

try {
  eval("var error = reference");
} catch (error) {
  e = error;
}

assertTrue(e.hasOwnProperty('stack'));

// Check that intercepting property access from toString is prevented for
// compiler errors. This is not specified, but allowing interception
// through a getter can leak error objects from different
// script tags in the same context in a browser setting.
var errors = [SyntaxError, ReferenceError, TypeError, RangeError, URIError];
var error_triggers = ["syntax error",
                      "var error = reference",
                      "undefined()",
                      "String.fromCodePoint(0xFFFFFF)",
                      "decodeURI('%F')"];
for (var i in errors) {
  var name = errors[i].name;

  // Monkey-patch prototype.
  var props = ["name", "message", "stack"];
  for (var j in props) {
    errors[i].prototype.__defineGetter__(props[j], fail);
  }
  // String conversion should not invoke monkey-patched getters on prototype.
  var error;
  try {
    eval(error_triggers[i]);
  } catch (e) {
    error = e;
  }
  assertTrue(error.toString().startsWith(name));

  // Deleting message on the error (exposing the getter) is fine.
  delete error.message;
  assertEquals(name, error.toString());

  // Custom properties shadowing the name are fine.
  var myerror = { name: "myerror", message: "mymessage"};
  myerror.__proto__ = error;
  assertEquals("myerror: mymessage", myerror.toString());

  // Custom getters in actual objects are welcome.
  error.__defineGetter__("name", function() { return "mine"; });
  assertEquals("mine", error.toString());

  // Custom properties shadowing the name are fine.
  var myerror2 = { message: "mymessage"};
  myerror2.__proto__ = error;
  assertEquals("mine: mymessage", myerror2.toString());
}

// Monkey-patching non-internal errors should still be observable.
function MyError() {}
MyError.prototype = new Error;
var errors = [Error, RangeError, EvalError, URIError,
              SyntaxError, ReferenceError, TypeError, MyError];
for (var i in errors) {
  errors[i].prototype.__defineGetter__("name", function() { return "my"; });
  errors[i].prototype.__defineGetter__("message", function() { return "moo"; });
  var e = new errors[i];
  assertEquals("my: moo", e.toString());
}


Error.prototype.toString = Object.prototype.toString;
assertEquals("[object Error]", Error.prototype.toString());
assertEquals(Object.prototype, Error.prototype.__proto__);
var e = new Error("foo");
assertEquals("[object Error]", e.toString());