existsOnDisk.js

var json = {
  "musicalNotes": {
    "fileLocation": ".",
    "extension": ".png",
    "filePairs": [
      {
        "existsOnDisk": false,
        "obverse": "c4.obverse",
        "reverse": "c4.reverse"
      },
      {
        "existsOnDisk": true,
        "obverse": "c5.obverse",
        "reverse": "c5.reverse"
      },
      {
        "existsOnDisk": true,
        "obverse": "c6.obverse",
        "reverse": "c6.reverse"
      }
    ]
  }
}