firebase.json

{
  "hosting": {
    "public": "public",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ],
    "headers": [
      {
        "source": "**",
        "headers": [
          {
            "key": "Access-Control-Allow-Origin",
            "value": "*"
          },
          {
            "key": "Access-Control-Allow-Methods",
            "value": "POST, GET, OPTIONS, HEAD"
          }
        ]
      },
      {
        "source": "**/**",
        "headers": [
          {
            "key": "Access-Control-Allow-Origin",
            "value": "*"
          },
          {
            "key": "Access-Control-Allow-Methods",
            "value": "POST, GET, OPTIONS, HEAD"
          }
        ]
      },
      {
        "source": "cert/*.json",
        "headers": [
          {
            "key": "Access-Control-Allow-Origin",
            "value": "*"
          },
          {
            "key": "Access-Control-Allow-Methods",
            "value": "POST, GET, OPTIONS, HEAD"
          },
          {
            "key": "Access-Control-Allow-Headers",
            "value": "*"
          }
        ]
      }
    ],
    "rewrites": [ {
      "source": "/metadata/**",
      "function": "metadata"
    }]
  },
  "functions": {
    "predeploy": [
      "npm --prefix \"$RESOURCE_DIR\" run lint",
      "npm --prefix \"$RESOURCE_DIR\" run build"
    ]
  }
}