Node project npm start error 404 Magi Ajax request 404

I follow the teaching video at this stage to do a front-end node project (I don"t know much about node). I am responsible for the implementation of the front-end page and interface development.
Environment deployment:
1. Node.js and npm
2 are installed. Downloaded the project source code
3. Installed the required dependency package
4. Imported the database and changed the database password
problem: when the npm start Times error 404, the front-end static page interface ajax request also reported an error 404. Localhost3000page shows no information

1. Why did this happen? Is it because my environment is not ready yet? Or does the project itself do not have this file? Please give me
Failed to load resource: net::ERR_CONNECTION_RESET

advice.
Javascript
Mar.21,2021
Is the

port sure to be the default?

lack of compiled program entry I'm afraid you don't have build, cut to the project root 

> npm build
> npm run dev

if it is a production environment, it is recommended to use pm2 to manage

package.json this is for building your node.js project, if there is not exists node_modules compiled node.js project mapping to your related project, then you can not run any way. You just need to build your project with package.json file, and run develop environment dev or product environment build.

run dev

Previous: Import the global Scripts, into Index.ejs and refer to it in a separate page, and run the lint report undefined.

Next: Use vue-video-player, to switch video sources in full-screen state, appear to jump out of full-screen and videojs reports an error

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1bf462c-31674.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1bf462c-31674.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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