JSON object is getting corrupted

I am using a JSON object on a project I am working on. I am doing many updates to this JSON file as it is my primary file to work with. I am using nodejs to handle requests and processes my file.

My JSON data looks something like this:

[
   { field1:123,
    field2:"Test",
    field3:"New",
    field4:"City",
   },
   { field1:"123",
    field2:"Test2",
    field3:"FILE to use",
    field4:"Assignment Token",
   }
]

Throughout its life cycle my files gets corrupted and a it show a similar pattern every time it gets corrupted. I tried to reduce as many number of call it is possible. The pattern it shows is as follows. Any ideas how to avoid this?

[
   { field1:123,
    field2:"Test",
    field3:"New",
    field4:"City",
   },
   { field1:"123",
    field2:"Test2",
    field3:"FILE to use",
    field4:"Assignment Token",
   }
]o use",field4:"Assignment Token",}]