BigInt are not supported in .deep.equal()

[SmashingQuasar]

Hey!

I am using the latest version of Chai and it appears if you try to deep equal an object that has a property of type BigInt, Chai will throw an Error.

Here is a code sample that should reproduce the issue (TypeScript):

import { describe, it } from "mocha";
import { expect } from "chai";

class Foo {
  private bar: BigInt = 0n;
}

describe("BigInt are not supported", (): void => {
  it("should work", (): void => {
    const instance: Foo = new Foo();
    const secondInstance: Foo = new Foo();

    expect(instance).to.deep.equal(secondInstance); // This will throw
  });
});

Support for BigInt was apparently added a while back but it seems it no longer works or deep.equal did not work.

[SmashingQuasar]

As a workaround for anyone encountering this issue, you add this to your runner pre-run script:

	// eslint-disable-next-line no-extend-native -- Chai does not support BigInt serialisation.
	Object.defineProperty(
		BigInt.prototype,
		"toJSON",
		{
			writable: false,
			enumerable: false,
			configurable: false,
			value: function(): string
			{
				// eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/restrict-template-expressions
				return `${this.toString()}n`;
			},
		}
	);

It's unclean but at least it works.

[43081j]

i tried the exact code in the first post and it seems to work fine for me

could you give some more info, like how you're building and running this test?

e.g. do you use ts-node or do you run the built JS? do you output commonjs or esm? etc etc

[SmashingQuasar]

i tried the exact code in the first post and it seems to work fine for me

could you give some more info, like how you're building and running this test?

e.g. do you use ts-node or do you run the built JS? do you output commonjs or esm? etc etc

Hey!

Thanks for your answer. To help understand this problem, I will create a repository aiming to replicate the issue with a few dependencies and code as possible and post it here. That way I will either find my own mistake or save you time instead of making you blindly look for the problem.