idea

Continuous rebuild for dev:

for general purpose

Use npm-watch. Add a watch section to package.json:

"watch": {
    "bns:server": {
    "patterns": "src",    
    "ignore": "src/client",
    "extensions": "ts"
    }
},

Add watch scripts: 

"scripts": {
// ...
    "watch": "npm-watch",
    "dev:server": "npm run watch bns:server",
    "bns:server": "npm run build:server && npm run start",
    "build:server": "tsc",
// ...

for webpack

Use NODE_ENV=development webpack --watch.

references