Rollup is injecting JS not supported by IE11 (is IE11 supported?)

[GordonSmith]

• Rollup Version: 2.27.1
• Operating System (or Browser): IE11
• Node Version (if applicable): NA
• Link to reproduction: https://repl.it/@GordonSmith/QuaintPlumUtilities

Expected Behavior

RollupJS should not inject JS which is unsupported by IE11

Actual Behavior

RollupJS is injecting Object.assign which is not supported in IE11

Generated code which includes Object.assign:

var _colorbrewer = /*#__PURE__*/Object.freeze(/*#__PURE__*/Object.assign(/*#__PURE__*/Object.create(null), colorbrewer$1, {
    'default': colorbrewer$1
}));

[GordonSmith]

FWIW, this is what tslib (typescript) uses to solve the same issue -

var __assign = function() {
    __assign = Object.assign || function __assign(t) {
        for (var s, i = 1, n = arguments.length; i < n; i++) {
            s = arguments[i];
            for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p)) t[p] = s[p];
        }
        return t;
    };
    return __assign.apply(this, arguments);
};

[shellscape]

I'd recommend injecting a polyfill into the bundle where needed, easily remedied from your end.

IE11 is end of life next year and the list of sites no longer supporting it is growing exponentially. Best to prepare now for no one supporting it in 11 months.

[GordonSmith]

@shellscape - while I agree with your sentiment re IE11, I am hitting this issue as both a consumer of bundles as well as a creator of bundles.

FWIW I have added pollyfills to code that I have control over and was simply reporting the issue here in an effort to help (I was a bit surprised to not see a similar report, or documentation saying IE11 no longer supported as of v2 etc.).

[lukastaegert]

This will finally be resolved in #4215