Bug 138857 – Updating a non-writable property of a coerced primitive object does not throw a TypeError exception in a strict mode

• Component: JavaScriptCore
• Status: RESOLVED INVALID

[Daejun Park]

In a strict mode, it should throw a TypeError exception, when attempting to update a non-writable property of a coerced primitive object, but Safari does not.

According to ES5, Section 8.7.2 PutValue (V, W), [[Put]] internal method, Step 2.a,
http://es5.github.io/#x8.7.2

the following code is supposed to throw a TypeError exception, since "x" is not writable in the coerced number object for "1":

"use strict";
Object.defineProperty(Number.prototype, "x", { "value" : 0, "writable" : false, "enumerable" : true, "configurable" : true });
1["x"] = 10; // 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]

I'm sorry for the noise. It turns out that I've missed how Web Inspector works. The above example works correctly when I wrapped the code with a function, ensuring the strict mode, as follows:

function f() {
  "use strict";
  Object.defineProperty(Number.prototype, "x", { "value" : 0, "writable" : false, "enumerable" : true, "configurable" : true });
  1["x"] = 10; // TypeError
}
f();

I close this issue.

Thanks,
Daejun