seems similar to the bug https://github.com/NodeBB/NodeBB/issues/3489 so you may just need to update your dependencies (rm -rf node_modules && npm cache clean && npm i).
That worked, thanks!
I want to add a new field "imgUrl" for each topic.
I modified composer.tpl and added a new input field "imgUrl" between "title" and "tags".
I also tried to modify post() in composer.js.
But when I press "submit", the text in "imgUrl" is replaced by the text in "title" and this topic is not saved.
Is there any hint for me to add a new field for each topic?
First of all we already have topic thumbnails you can enable it from the ACP.
If that isn't enough you can take a look at the code that makes it work and duplicate that.