Test functions for javascript:

// TODO: Add your tests here
// Starting from Node 10.x, [Mocha](https://mochajs.org) is used instead of our custom test framework.
// [Codewars' assertion methods](https://github.com/Codewars/codewars.com/wiki/Codewars-JavaScript-Test-Framework)
// are still available for now.
//
// For new tests, using [Chai](https://chaijs.com/) is recommended.
// You can use it by requiring:
//     const assert = require("chai").assert;
// If the failure output for deep equality is truncated, `chai.config.truncateThreshold` can be adjusted.

describe("Solution", () => {
  it("should test for something", () => {
    Test.assertDeepEquals(anagrams("abba", ["aabb", "abcd", "bbaa", "dada"]), [
      "aabb",
      "bbaa",
    ]);
  });

  it("should test for something", () => {
    Test.assertDeepEquals(
      anagrams("racer", ["crazer", "carer", "racar", "caers", "racer"]),
      ["carer", "racer"]
    );
  });

  it("should test for something", () => {
    Test.assertDeepEquals(anagrams("laser", ["lazing", "lazy", "lacer"]), []);
  });
});

You're all mutating the array it seems.

You're right, it is the same error for me

I figured out the same issue, in C#

It should not happen.