symbol build option causes memory leak on IE

[Rawld Gill]

The functionality in #13352 introduces named function expressions (NFEs) which cause memory leaks on IE (see ​http://kangax.github.com/nfe/). A named function expression looks like this:

var f = function g(){};

In IE, this will actually create two different functions and assign one to "f" and one to "g". Since they both reference each other through a closure, IE won't garbage collect them. In order for IE to garbage collect them, you have to null out the "named" function:

var f = function g(){};
var g = null;

The leaks are cleared up when the browser refreshes or you close the browser, but this is still a leak on single-page applications since you can't reclaim the memory except by navigating away from the page.

This feature is opt-in and would likely *not* be used for released code. Also, the implementation of this feature did not change in 1.7 compared to prior versions.

[ben hockey]

i'm wondering if we shouldn't just add some kind of log message during a build to warn developers of this problem and then close this ticket. i'm not sure there's anything we can do to fix it.

[Rawld Gill]

In [29192]:

added warning about leaks on IE when building with symbols; fixes #13563; !strict