Version

3.1.0-beta.3

Steps to reproduce

Update vue-2 project according to this guide -> https://github.com/vuejs/vue-next/tree/master/packages/vue-compat

What is expected?

Project to run with no errors or at least errors would be readable.

What is actually happening?

I'm getting strats[key] is not a function error and I can't figure out where is it coming from.

Can you guys help me to figure out how to fix it? Detailed error below.

vue.runtime.esm-bundler.js?1786:4724 Uncaught (in promise) TypeError: strats[key] is not a function
    at mergeOptions (vue.runtime.esm-bundler.js?1786:4724)
    at eval (vue.runtime.esm-bundler.js?1786:4710)
    at Array.forEach (<anonymous>)
    at resolveMergedOptions (vue.runtime.esm-bundler.js?1786:4710)
    at $options (vue.runtime.esm-bundler.js?1786:9305)
    at Object.get (vue.runtime.esm-bundler.js?1786:9438)
    at Proxy.beforeCreate (vue-router.esm.js?8c4f:550)
    at callWithErrorHandling (vue.runtime.esm-bundler.js?1786:1343)
    at callWithAsyncErrorHandling (vue.runtime.esm-bundler.js?1786:1352)
    at callHookWithMixinAndExtends (vue.runtime.esm-bundler.js?1786:4626)

It seemed you have configured a custom option merge strategy via app.config.optionMergeStrategies but it's not a function.

Next time, please use the forum or the Discord chat to ask questions.

No, I haven't. But thanks for the answer, I will use the forum from now on