Currently Heroku reinstalls all dependencies each time I deploy my app. It can possibly break something if a new version of a dependency has a bug or not compatible with my current setup. Is there a way to tell heroku to download dependencies only when I change version in the package.js (just like they do it on dotCloud)?
Unless there is a bug in Heroku, the way to block a package is to use a specific version of your dependencies inside your package.json. Take a look at the node.js page.
sample package.json:
{
"name": "appname",
"version": "0.0.1",
"dependencies": {
"express": "2.5.8"
},
"engines": {
"node": "0.8.x",
"npm": "1.1.x"
}
}