Regex exec problems in simulated IE8

[IanVS]

I've hit a strange problem while trying to add useBuiltins: 'usage' to an app that is forced to support IE8 as well as newer IE in IE8 compatibility mode. I have multiple webpack entrypoints that get loaded on a single page (I know that's weird, but it's been working that way for a long time). When I try to add core-js via babel, I find that the regex polyfill is running twice, and it seems to assume that it's only ever going to run one time. Specifically, I'm referring to this line:

core-js/packages/core-js/internals/regexp-exec.js

Line 9 in 8b121e3

var nativeReplace = String.prototype.replace;

nativeReplace is assumed to always be native, and seemingly because of this assumption, IE8 in compat mode enters an infinite loop and runs out of memory down here:

core-js/packages/core-js/internals/regexp-exec.js

Line 76 in 8b121e3

nativeReplace.call(match[0], reCopy, function () {

if it has already been polyfilled. I'm not sure why, but it seems to be okay in real IE8. For now I'm going to work on preventing this from being called twice, but I wanted to at least open the issue in case it warrants a look. Thanks!

[IanVS]

Thanks a ton for addressing this so quickly!