Prettier 1.9.0
Playground link

# Options (if any):
{
  "singleQuote": true,
  "trailingComma": "es5"
}

Input:
See playground

Output:

[error] Invalid printWidth value.
[error] Expected an integer, but received: "off"

Expected behavior:
No printWidth config needed.

I do not get this error with the following config:

{
  "singleQuote": true,
  "trailingComma": "es5",
+  "printWidth": 80
}