Date.now() cannot be faked when using @babel/runtime-corejs*

• FakeTimers version : 6.0.1
• Environment : node v10.19.0, macOS v10.15.4
• Example URL:
• Other libraries you are using: See below.

What did you expect to happen?

Date.now() returns 0

What actually happens

Date.now() returns current timestamp.

How to reproduce

1. Configure project to use @babel/runtime-corejs3:

   package.json

   {
     "name": "test",
     "version": "1.0.0",
     "description": "",
     "main": "index.js",
     "scripts": {
       "test": "echo \"Error: no test specified\" && exit 1"
     },
     "author": "",
     "license": "ISC",
     "devDependencies": {
       "@babel/core": "^7.9.0",
       "@babel/plugin-transform-runtime": "^7.9.0",
       "@babel/preset-env": "^7.9.0",
       "@babel/register": "^7.9.0"
     },
     "dependencies": {
       "@babel/runtime": "^7.9.2",
       "@babel/runtime-corejs3": "^7.9.2",
       "@sinonjs/fake-timers": "^6.0.1"
     }
   }
   

   babel.config.js

   module.exports = {
     "presets": ["@babel/preset-env"],
     "plugins": [
       ["@babel/plugin-transform-runtime", { "corejs": 3 }]
     ]
   }
   

2. Create index.js as follows:

   import FakeTimers from '@sinonjs/fake-timers'
   
   FakeTimers.install()
   
   console.log(new Date().getTime())
   console.log(Date.now())
   

3. Execute the script:

   > node -r @babel/register index.js
   0
   1585877900883
   

The last line of output should be 0, but it is the current timestamp instead.

Note: can also be reproduced using (deprecated) @babel/runtime-corejs2.

[fatso83]

OK, this was easy. Just run babel to inspect the output and it is immediatly clear:

$ npm i @babel/cli 
...

$ $(npm bin)/babel index.js 
"use strict";

var _interopRequireDefault = require("@babel/runtime-corejs3/helpers/interopRequireDefault");

var _now = _interopRequireDefault(require("@babel/runtime-corejs3/core-js-stable/date/now"));

var _fakeTimers = _interopRequireDefault(require("@sinonjs/fake-timers"));

_fakeTimers["default"].install();

console.log(new Date().getTime());
console.log((0, _now["default"])());

You corejs3 is replacing Date.now by a strictly bound reference to @babel/runtime-corejs3/core-js-stable/date/now. We cannot do anything about that, basically, but maybe you can find a way to configure core-js to not do this.

[fatso83]

Screw that. I decided to just run your test case (very easy to do, so great job, btw!) and I had misunderstood what was going on: fake timers ARE being installed, it seems, it’s just that it does not seem to be working for that one call. The other is fine. I’ll inspect.