npm scripts: is there a cross platform conditional statement?

I'm attempting to move an npm package over from being *nix dependent to being cross platform. I have the following scripts entry in the package.json:

"scripts": {
    "build": "rimraf dist/ && tsc",
    // other entries
    "prepublish": "if [ ! $SKIP_PREPUBLISH ]; then npm run build; fi"
  },

I want to take the if [ ! $SKIP_PREPUBLISH ]; then npm run build; fi and make that cross platform. Is there a way to do that?