readArguments

Read an argument array and extract metadata, error and message arguments.

Reference

• LogArguments

declare function readArguments(args: unknown[]): LogArguments;

Constraints

• args must be an array of arguments.
• The first argument must be a string, an error, or an object
• If the first argument is a string, all arguments will be treated as message template arguments, meta will be an empty object
• If the first argument is an error, meta will be an empty object, error will be an error, and other arguments will be treated as message template arguments
• If the first argument is an object
  • If it has err field, meta will be an object with all fields except err, error will be an error, other arguments will be treated as message template arguments
  • Otherwise, meta will be an object with all fields, error will be undefined, other arguments will be treated as message template arguments

Examples

// Strings

readArguments('hello'); // -> [ ['hello'], {} ]
readArguments('hello %s', 'world'); // -> [ ['hello %s', 'world'], {} ]
readArguments('hello %s %d %j', 'world', 1, { id: 2 }); // -> [ ['hello %s %d %j', 'world', 1, { id: 2 }], {} ]

// Additional fields

readArguments({ id: 2 }); // -> [ [], { id: 2 } ]
readArguments({ id: 2 }, 'hello'); // -> [ ['hello'], { id: 2 } ]
readArguments({ id: 2 }, 'hello %s', 'world'); // -> [ ['hello %s', 'world'], { id: 2 } ]

// Errors

readArguments(myError); // -> [ ['my error'], {}, myError ]
readArguments({ err: myError }); // -> [ ['my error'], {}, myError ]
readArguments({ err: myError, id: 2 }); // -> [ ['my error'], { id: 2 }, myError ]
readArguments({ err: myError, id: 2 }, 'hello'); // -> [ ['hello'], { id: 2 }, myError ]
readArguments({ err: myError, id: 2 }, 'hello %s', 'world'); // -> [ ['hello %s', 'world'], { id: 2 }, myError ]

LogArguments

Compact tuple parsed log arguments:

1. messageFragments - array of message fragments, where a first element is expected to be a format template which will be passed to printf function with the rest of the arguments as a replacement list
2. meta - object with fields, which will be merged with the first argument
3. error - can contain an error

export type LogArguments = [messageFragments: unknown[], meta: AnyObj, error?: Error];

Related

• createLoggerFactory API
• Formatting
• Metadata