npm ERR! missing script: build code example

Example 1: npm ERR! missing script: start

"scripts": {
   "start": "node app.js"
},

Example 2: npm ERR! missing script: build:dev

{
  "name": "testapp",
  "version": "1.0.0",
  "description": "",
  "scripts": {
    "dev": "echo This is the DEV script",
    "abc": "echo This is the abc script",
    "xyz": "echo This is the xyz script",
    "start":"echo This is the special start script"
  }
}