brainmassage questions

• How can I check if the component is unmounted in a functional component?
• The attribute value is undefined for the annotation type Produces for "MediaType.APPLICATION_JSON"
• npm run dev command does not work on vuejs' hackernews example
• Is there a way in Jackson to check if a JSON string compatible with a POJO?
• Why would I need template engines like Jade or EJS on the backend?

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