__spread does not work in IE11

This TypeScript code (a Jasmine test):

describe("array spread operator", function() {
    it('should be able to spread arguments', function() {
        let argumentsArray;
        function testFunction() {
            argumentsArray = [...arguments];
        }
        (testFunction as any)(1, 2, 3);
        expect(argumentsArray).toEqual([1, 2, 3]);
    });
});

runs successfully in browsers but IE. In IE11, it fails with:

Expected $.length = 1 to equal 3.
Expected $[0] = [object Arguments] to equal 1.
Expected $[1] = undefined to equal 2.
Expected $[2] = undefined to equal 3.

I can see the ... array spread operator gets built into a call for helper __spread, thus submitting the issue here.

Browsers I tried:

• Chrome 76.0.3809.100 64bit
• Opera 62.0.3331.116
• Firefox Quantum 68.0.1 64-bit
• Internet Explorer 11.309.16299.0
• Microsoft Edge 41.16299.248.0

[anton-bot]

The solution is to polyfill the Symbol.

import 'core-js/features/symbol';

Source: https://www.leereamsnyder.com/blog/new-skool-uniq-in-internet-explorer

[nvirth]

We recently updated TSC from 4.1.2 to 4.4.4, where we could see diffing the built JS before and after the TSC upgrade, that lot of __spread usages have been replaced with __spreadArray. After the upgrade, the above initial test case successfully runs in IE11.