debugger
Here is part of my package.json:
"scripts": {
    "build": "skpm-build",
    "build-production": "cross-env NODE_ENV=production skpm-build",
    ...
}
In Safari, I go to Develop > name of my machine > Automatically Show Web Inspector for JSContexts and enable Automatically Pause Connecting to JSContext. In addition, there is a "debugger" in my code.
When the command is "npm run build", the JavaScript context pause in debugger position, then I can use breakpoints in safari.  But when the command is "npm run build-production", the JavaScript context does not pause. so I can not see my code and can not use breakpoints in safari.