SCRIPT5045: Assignment to read-only properties is not allowed in strict mode IE11

[varadharajan007]

when try to open my angular2 project in IE11, i am getting this error

"SCRIPT5045: Assignment to read-only properties is not allowed in strict mode
vendor.bundle.js (8031,5)".

In vendor.bundle.js file ,
Debugger is point on this function
--> ObservableArray.prototype.find = function (predicate, thisArg, fromIndex) {
if (fromIndex === void 0) { fromIndex = 0; }
var idx = this.findIndex.apply(this, arguments);
return idx === -1 ? undefined : this.get(idx);
};

please let me know about solutions.

[zloirock]

I don't see anything related core-js here. ObservableArray is not a part of core-js.

[mweststrate]

See also: mobxjs/mobx#1028 (comment). The MDN official polyfill incorrectly creates a non-configurable, non-writable property. (Just submitted an issue to MDN to fix that).

If core-js also introduces Array.prototype.find with a property descriptor that is not: { configurable: true, enumerable: false, writable: false}, than this could be an issue.

Since I am completely unfamiliar with core-js, I don't know how to check that quickly (couldn't find it in the source code)

[zloirock]

@mweststrate by the spec, Array.prototype.find descriptor should be {writable: true, enumerable: false, configurable: true} and core-js use it. Because of usagedefineProperty in core-js for polyfilling Array.prototype.find, this incorrect descriptor from MDN polyfill should not be a problem. How it's related this issue?

[mweststrate]

I don't know if it is related, hence the question :) I wanted to check that, but didn't know how (I don't have a project using core-js in its build lingering around anywhere, and searching the sources didn't give a clue), so figured I could ask instead :-).

I got this issue reported a few times, but most people themselves hardly know where their polyfills are coming from, so wanted to double check that core-js isn't causing it.

Thanks for the info!