Sync with upstream @ 4d01fc20

[javascript-translate-bot]

This PR was automatically generated to merge changes from en.javascript.info at 4d01fc20

Conflicted files in this PR have labels ">>>..." with both sides of conflict. If you merge this PR, you'll need to examine the listed files and resolve conflicts.

Alternatively, you can close this PR and merge conflicting changes manually.

The following files have conflicts and may need updates of the translations:

• [ ] 1-js/02-first-steps/04-variables/article.md
• [ ] 1-js/02-first-steps/13-while-for/article.md
• [ ] 1-js/02-first-steps/15-function-basics/article.md
• [ ] 1-js/04-object-basics/06-constructor-new/1-two-functions-one-object/task.md
• [ ] 1-js/04-object-basics/09-object-toprimitive/article.md
• [ ] 1-js/05-data-types/02-number/article.md
• [ ] 1-js/05-data-types/09-keys-values-entries/article.md
• [ ] 1-js/07-object-properties/01-property-descriptors/article.md
• [ ] 1-js/09-classes/04-private-protected-properties-methods/article.md
• [ ] 1-js/10-error-handling/2-custom-errors/article.md
• [ ] 1-js/11-async/01-callbacks/article.md
• [ ] 1-js/11-async/05-promise-api/article.md
• [ ] 1-js/12-generators-iterators/1-generators/article.md

To merge changes manually (instead of merging this PR):

1. Add remote upstream that links to the English version (only needs to be done once)
   • git add remote upstream https://github.com/javascript-tutorial/en.javascript.info
2. Commit all current work locally and git checkout master
3. Pull the recent changes from the English version:
   • git pull upstream master
4. Deal with the conflicts. If a conflict touches a few lines, then just fix it. Otherwise, following commands can help:
   • Checkout your (translated) version of a file/folder at the given path (removes all upstream changes):
     • git checkout --ours <path>
   • See the diff, what changed in the upstream file since branches diverged:
     • git diff --word-diff master...upstream/master <path> (please note: three dots in the command)
   • Then you can examine the changes in upstream and add them manually
5. When conflicts resolved, commit them and git push origin master

This PR will be closed and replaced with a new one in a few days.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
3 out of 6 committers have signed the CLA.

:white_check_mark: joaquinelio
:white_check_mark: odsantos
:white_check_mark: iliakan
:x: siimpragi
:x: shvchk
:x: msmilkshake
_{You have signed the CLA already but the status is still pending? Let us recheck it.}