firebase.json

{
    "database": {
      "rules": "database.rules.json"
    },
    "firestore": {
      "rules": "firestore.rules",
      "indexes": "firestore.indexes.json"
    },
    "hosting": {
      "public": "./build",
      "cleanUrls": true,
      "rewrites": [{
        "source": "/**",
        "function": "prerender"
      }],
      "ignore": [
        "/test/**",
        "bower.json",
        "database.rules.json",
        "firebase.json",
        "README.md"
      ],
      "headers": [
        {
          "source": "**",
          "headers": [
            {
              "key": "X-Content-Type-Options",
              "value": "nosniff"
            },
            {
              "key": "X-Frame-Options",
              "value": "DENY"
            },
            {
              "key": "X-XSS-Protection",
              "value": "1; mode=block"
            },
            {
              "key": "Referrer-Policy",
              "value": "same-origin"
            }
          ]
        }
      ]
    },
    "functions": {
      "predeploy": [
        "npm run predeploy",
        "npm --prefix ./functions run build"
      ]
    }
  }