caching for static contents using firebase headers

firebase.json

{
  "functions": {
    "predeploy": [
      "node predeploy.js"
    ],
    "source": "functions"
  },
  "firestore": {
    "rules": "config/firestore.rules",
    "indexes": "config/firestore.indexes.json"
  },
  "hosting": {
    "public": "static",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**",
      "./__sapper__",
      "./src"
    ],
    "rewrites": [
      {
        "source": "**",
        "function": "ssr"
      }
    ],
    "headers": [ {
      "source": "**",
      "headers": [ {
        "key": "Cache-Control",
        "value": "public, max-age=604800, must-revalidate, s-maxage=604800, proxy-revalidate, stale-while-revalidate=86400, stale-if-error=604800"
      } ]
    } ]
  },
  "storage": {
    "rules": "config/storage.rules"
  }
}