[Documentation] JavaScript Environment Requirements

[jenweber]

This issue was originally opened by @EWhite613 in emberjs/ember.js#20471 and transferred to this repository. Copy-pasted content:

With the new Ember browser support policy it's difficult to see a way forward with Ember for apps that need to support legacy browser versions outside that statement.

Ember should have a JavaScript Environment Requirements like React did, and other libraries have. And include in changelogs when new features are used (react example).

This way those that need to support older legacy browser versions at least have an idea what they need to polyfill (or if they can even polyfill).

[jenweber]

Whoever picks up this ticket would need to do the following. This is not a beginner task, and requires knowledge of browser compatibility.

• Determine what needs to be documented
• Collaborate with the Framework team via Discord to check if the list is correct
• Add the content to https://emberjs.com/browser-support/
• Determine how and when to update this page. When would contributors know to add something? Document it in https://github.com/ember-learn/handbook/blob/main/ember-releases.md