Issue Description

I'm using Webpack with core-js polyfill in my Node.js project relying on Sequelize library. I decided to make an earlier migration from Sequelize 5 to Sequelize 6 but was unable to make it working to due this error:

/home/ezze/Development/geobase/node_modules/lodash/lodash.js:11927
        throw new Error(CORE_ERROR_TEXT);
        ^

Error: Unsupported core-js use. Try https://npms.io/search?q=ponyfill.
    at Function.isNative (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:11927:15)
    at _.mergeWith (/home/ezze/Development/geobase/node_modules/sequelize/lib/utils.js:54:42)
    at baseMergeDeep (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3643:11)
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:3603:11
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:4905:15
    at baseMerge (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3600:7)
    at baseMergeDeep (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3689:9)
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:3603:11
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:4905:15
    at baseMerge (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3600:7)
    at baseMergeDeep (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3689:9)
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:3603:11
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:4905:15
    at baseMerge (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3600:7)
    at baseMergeDeep (/home/ezze/Development/geobase/node_modules/lodash/lodash.js:3689:9)
    at /home/ezze/Development/geobase/node_modules/lodash/lodash.js:3603:11

What are you doing?

Upgrading Sequelize 5 => 6. I narrowed down the problem and created a repo to reproduce it. The issue is caused by _.isNative() function that is incompatible with core-js and is used by mergeDefaults utility function of Sequelize.

This method can't reliably detect native functions in the presence of the core-js package because core-js circumvents this kind of detection. Despite multiple requests, the core-js maintainer has made it clear: any attempt to fix the detection will be obstructed. As a result, we're left with little choice but to throw an error. Unfortunately, this also affects packages, like babel-polyfill, which rely on core-js.

What do you expect to happen?

The code working in Sequelize 5 to work in Sequelize 6.

What is actually happening?

An error

Error: Unsupported core-js use. Try https://npms.io/search?q=ponyfill.

is thrown.

Environment

• Sequelize version: 6.0.0-beta.6
• Node.js version: 10.21.0
• Operating System: Ubuntu 18.04 LTS

How does this problem relate to dialects?

• I think this problem happens regardless of the dialect.
• I think this problem happens only for the following dialect(s):
• I don't know, I was using PUT-YOUR-DIALECT-HERE, with connector library version XXX and database version XXX

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don't know how to start, I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.