Why ts-node index.ts doesn't work, but ts-node through npm run works?

Question

So I got a project for a long time now.

I decided to switch to typescript.

I installed npm install ts-node

When I do ts-node src/index.ts it tells me it doesn't know any ts-node command but when I run npm run run which looks like this:

  scripts": {
    "run": "ts-node src/index.ts"
  },

It works fine.

After I installed ts-node globally it works, but is there a way to run it without installing it globally?