What does 'locations' refer to in GraphQL errors?

Question

I'm working through a GraphQL Node/Prisma server tutorial and encountered an error due to something wrong in my code. I've solved the error but I want to understand the error message, in particular, what does locations refers to? That is, I have a location of line 2, column 3, but line 2, column 3 of what? The relevant method in my code (signup, in this case)? Of my mutation?

// error message 
{
  "data": {
    "signup": null
  },
  "errors": [
    {
      "message": "secretOrPrivateKey must have a value",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "signup"
      ]
    }
  ]
}

Answer 1

Just like path, locations refers to where inside your GraphQL document the error occurred. You can see this for yourself using something like the SWAPI GraphQL endpoint. We can trigger a validation error by requesting a field that doesn't exist:

{
  allFilmz
}

The resulting error has this locations array:

[
  {
    "line": 2,
    "column": 3
  }
]

That's because the offending field is on line 2, starting with column 3. If we instead send:

{allFilmz}

we get:

[
  {
    "line": 1,
    "column": 2
  }
]

Generally, the path of the error will be more informative than the locations, but the path won't exist when there are syntax errors in your document -- in those cases, the locations are the only thing you can use to track down where your syntax error occurred.

Word of caution if using GraphQL Playground -- unlike GraphiQL, Playground will strip out comments and format your request before sending it, so the locations may not match what you see in the Playground UI.