Bug 138858 – Updating an immutable binding does not throw a TypeError exception in a strict mode

• Component: JavaScriptCore
• Status: NEW

[Daejun Park]

In a strict mode, it should throw a TypeError exception, when attempting to update an immutable binding, but Safari does not.

According to ES5, Section 10.2.1.1.3 SetMutableBinding (N,V,S), Step 4,
http://es5.github.io/#x10.2.1.1.3

the following code is supposed to throw a TypeError exception, since "g" is an immutable binding inside the function body (according to ES5, Section 13 Function Definition, Step 3 of the third block).

"use strict";
var f = function g() {
  g = 0;
}; 
f(); // TypeError

However, Safari does not report any exception, while Firefox correctly throws a TypeError exception.

I've tested this using the Web Inspector console of Safari 7.0.4.

Thanks,
Daejun

[Daejun Park]

For your information, this issue appears even if I wrapped the code as follows:
function x() {
  "use strict";
  var f = function g() {
    g = 0;
  };
  f(); // TypeError
}
x();

Also, I reported this issue for v8:
https://code.google.com/p/v8/issues/detail?id=3704

but it turns out that it was duplicate:
https://code.google.com/p/v8/issues/detail?id=2243

and it will not be fixed because ES6 will consider this as a syntax error.

Do you have the same decision for this?

[Radar WebKit Bug Importer]

<rdar://problem/19032831>