141184 2015-02-02 19:05:33 -0800 REGRESSION: Function declaration inside a function and using the same name as an argument to the containing function no longer takes precedence over the argument 2015-02-09 09:52:50 -0800 1 1 1 Unclassified WebKit JavaScriptCore 528+ (Nightly build) Unspecified OS X 10.10 NEW InRadar P2 Normal --- 1 rob webkit-unassigned fpizlo ggaren webkit-bug-importer oldest_to_newest 1066320 0 rob 2015-02-02 19:05:33 -0800 Using the latest WebKit Nightly (r179474), I ran into a problem using code like the following: ``` (function(Thing) { Thing.whatever = "This breaks."; function Thing() { return this; } })() ``` An exception is thrown on line 2 above, when trying to assign to `Thing.whatever`. The exception is “TypeError: undefined is not an object (evaluating 'Thing.whatever = "This breaks."')“ It seems that, on line 2, `Thing` evaluates to the first argument of the containing function (which is undefined) instead of the function defined in line 3. This differs from the currently shipping version of Safari, where `Thing` on line 2 evaluates to the function declaration instead of to `undefined`. A quick perusal of section “10.5 Declaration Binding Instantiation” in the ECMA-262 spec _seems_ like the new behavior is correct, though I’m honestly not sure I’m reading it right. However, this behavior differs from previous builds of JSC and from many other JS engines (V8, Spidermonkey). It also breaks code existing in the wild — I encountered this while browsing a site built using Instapaper’s web app (http://instapaper.com), which I believe is using Browserify, which creates code like the above example. 1066324 1 rob 2015-02-02 19:20:53 -0800 Well, in the process of writing a test for this, it seems like this only fails when the inspector is open, so this might not actually be JSC, but instead something about the web inspector. Still not sure why Instapaper doesn’t work in WebKit Nightly; assuming it’s unrelated to this (and hard to determine since the inspector can’t be open!) :( 1066391 2 rob 2015-02-03 01:41:39 -0800 OK! This took a fair amount of poking before I finally narrowed it down. The cause of the problem I was seeing on Instapaper was actually code in the form: ``` (function(Thing) { Thing.whatever = "This breaks."; function Thing() { // referencing `Thing` in this inner scope here is what does it Thing; } })() ``` It seems like referencing `Thing` inside the `Thing` function inside a function with `Thing` as an argument (wow) causes `Thing` in the outer function to reference the argument instead of the function declaration. As far as what I was seeing with the inspector open, I have no idea whether it was related or completely different. Whether or not the cause is the same, the symptoms are. 1066392 3 245929 rob 2015-02-03 01:48:00 -0800 Created attachment 245929 Simple test case for function declaration names vs. argument names 1066501 4 webkit-bug-importer 2015-02-03 11:05:37 -0800 <rdar://problem/19702564> 1067838 5 rob 2015-02-09 09:52:50 -0800 FWIW, I have encountered this issue on several more sites in regular browsing. It may be an odd construction, but it’s definitely a real-world problem. 245929 2015-02-03 01:48:00 -0800 2015-02-03 01:48:00 -0800 Simple test case for function declaration names vs. argument names function-declaration-vs-argument-name-resolution.html text/html 1549 rob PCFET0NUWVBFIGh0bWw+CjxodG1sPgogIDxoZWFkPgogICAgPG1ldGEgY2hhcnNldD0idXRmLTgi IC8+CiAgICA8dGl0bGU+RnVuY3Rpb24gZGVjbGFyYXRpb25zIHNob3VsZCB0YWtlIHByZWNlZGVu Y2Ugb3ZlciBmb3JtYWwgYXJndW1lbnRzIGluIHRoZSBzYW1lIHNjb3BlLjwvdGl0bGU+CiAgICA8 c3R5bGUgdHlwZT0idGV4dC9jc3MiPgogICAgICAucGFzcyB7CiAgICAgICAgYmFja2dyb3VuZDog Z3JlZW47CiAgICAgICAgY29sb3I6IHdoaXRlOwogICAgICB9CiAgICAgIC5mYWlsIHsKICAgICAg ICBiYWNrZ3JvdW5kOiByZWQ7CiAgICAgICAgY29sb3I6IHdoaXRlOwogICAgICB9CiAgICA8L3N0 eWxlPgogIDwvaGVhZD4KICA8Ym9keT4KICAgCiAgICA8cD4KICAgICAgV2hlbiBhIGZ1bmN0aW9u IGlzIDxlbT5kZWNsYXJlZDwvZW0+IHVzaW5nIHRoZSBzYW1lIG5hbWUgYXMgYW4gYXJndW1lbnQK ICAgICAgb2YgYSBmdW5jdGlvbiBjb250YWluaW5nIHRoZSBkZWNsYXJhdGlvbiA8ZW0+YW5kPC9l bT4gdGhlIGlubmVyIG5hbWVkCiAgICAgIGZ1bmN0aW9uIGNvbnRhaW5zIGEgcmVmZXJlbmNlIHRv IHRoYXQgc2FtZSBuYW1lLCB0aGUgbmFtZSBzaG91bGQKICAgICAgcmVzb2x2ZSB0byB0aGUgdmFs dWUgb2YgdGhlIGRlY2xhcmVkIGZ1bmN0aW9uLCBub3QgdGhlIGFyZ3VtZW50LiBGb3IKICAgICAg ZXhhbXBsZSwgaW4gdGhlIGZvbGxvd2luZyBjb2RlIHNhbXBsZSwgPGNvZGU+VGhpbmc8L2NvZGU+ IHNob3VsZCByZXNvbHZlCiAgICAgIHRvIHRoZSA8Y29kZT5UaGluZzwvY29kZT4gPGVtPmZ1bmN0 aW9uPC9lbT4sIG5vdCB0aGUgPGNvZGU+VGhpbmc8L2NvZGU+IGFyZ3VtZW50OgogICAgPC9wPgog ICAgCjxwcmU+PGNvZGU+ZnVuY3Rpb24oVGhpbmcpIHsKICBUaGluZy53aGF0ZXZlciA9ICJUaGlz IGJyZWFrcy4iOwogIGZ1bmN0aW9uIFRoaW5nKCkgewogICAgVGhpbmc7CiAgfQp9PC9jb2RlPjwv cHJlPgoKICAgIDxwIGlkPSJwYXNzLWZhaWwiPjwvcD4KICAgCiAgICA8c2NyaXB0IHR5cGU9InRl eHQvamF2YXNjcmlwdCI+CiAgICAgIHZhciBhcmd1bWVudFZhbHVlID0ge307CiAgICAgIChmdW5j dGlvbihUaGluZykgewogICAgICAgIFRoaW5nLndoYXRldmVyID0gIlRoaXMgYnJlYWtzLiI7CiAg ICAgICAgZnVuY3Rpb24gVGhpbmcoKSB7CiAgICAgICAgICBUaGluZzsKICAgICAgICB9CiAgICAg IH0pKGFyZ3VtZW50VmFsdWUpOwogICAgICAKICAgICAgdmFyIHBhc3NGYWlsID0gZG9jdW1lbnQu Z2V0RWxlbWVudEJ5SWQoInBhc3MtZmFpbCIpOwogICAgICBpZiAoYXJndW1lbnRWYWx1ZS53aGF0 ZXZlciA9PT0gIlRoaXMgYnJlYWtzLiIpIHsKICAgICAgICBwYXNzRmFpbC5pbm5lckhUTUwgPSAi RkFJTCI7CiAgICAgICAgcGFzc0ZhaWwuY2xhc3NOYW1lID0gImZhaWwiOwogICAgICB9CiAgICAg IGVsc2UgewogICAgICAgIHBhc3NGYWlsLmlubmVySFRNTCA9ICJQQVNTIjsKICAgICAgICBwYXNz RmFpbC5jbGFzc05hbWUgPSAicGFzcyI7CiAgICAgIH0KICAgIDwvc2NyaXB0PgogCiAgPC9ib2R5 Pgo8L2h0bWw+Cg==