Bug 141670 – Descriptor of Function.arguments is inconsistent

• Component: JavaScriptCore
• Status: NEW

[Joseph Pecoraro]

* SUMMARY
Descriptor of Function.arguments is inconsistent. Sometimes it is a value, sometimes it is a getter/setter. This doesn't seem expected.

  js> Object.getOwnPropertyDescriptor(function(){}, "arguments")
  < {value: null, writable: false, enumerable: false, configurable: false}

  js> Object.getOwnPropertyDescriptor(function(){}.bind(this), "arguments")
  < {get: function, set: function, enumerable: false, configurable: false}

Also, it is possible that "arguments" should not be on the instance but actually on Function.prototype.

[Joseph Pecoraro]

Note, this affects Web Inspector. We look at descriptors when expanding objects. When the "arguments" property getter is invoked outside of an invocation of the function it produces an error:

  js> (function(){}).bind(this).arguments
  < TypeError: Type error

So when inspector tries to show the value of "arguments" in object expansion, we encounter the errors. It is a bit unfortunate and we may want to workaround this.

  js> dir(function(){}.bind(this))
  < function () { [native code] }
      arguments: [Exception: TypeError: Type error]
      caller: [Exception: TypeError: Type error]
      length: 0
      name: ""
      __proto__: function () {