feat(log): Added support for structured JSON logging

[syhol]

Implementing a solution for this issue: #3394

What is it?
Lets you configure the logger to emit structured json logs that will play nicely with log aggregators

Why do it?
People like structured json logs:

• https://stackify.com/what-is-structured-logging-and-why-developers-need-it/
• https://sematext.com/glossary/structured-logging/
• https://www.loggly.com/use-cases/what-is-structured-logging-and-how-to-use-it/

TLDR; Easier parsing makes it more reliable, cheap, and fast to gain insight into your logs, whether thats for monitoring, root cause analysis, or business intelligence.

What does it look like?

import * as log from "https://deno.land/std@$STD_VERSION/log/mod.ts";

log.setup({
  handlers: {
    default: new log.handlers.ConsoleHandler("DEBUG", {
      formatter: log.formatters.jsonFormatter,
      useColors: false,
    }),
  },
});

log.info("Hey");
// > {"level":"INFO","datetime":1702481922294,"message":"Hey"}

log.info("Hey", { product: "nail" });
// > {"level":"INFO","datetime":1702484111115,"message":"Hey","args":{"product":"nail"}}

log.info("Hey", 1, "two", [3, 4, 5]);
// > {"level":"INFO","datetime":1702481922294,"message":"Hey","args":[1,"two",[3,4,5]]}

The changes include:

• A new log/formatters.ts module with the new jsonFormatter function
  • Other formatters in future could include logfmt and maybe protobufs
  • DEFAULT_FORMATTER and FormatterFunction could be moved here
• Most log aggregators I've worked with didn't like colour codes, so ConsoleHandler now has a new optional property in its constructor parameter useColors?: boolean that defaults to true, keeping backwards compatibility. Only when explicitly set to false will the handler skip applying colours.
  • I could have created a new handler but I couldn't think of a good name name.
• Exporting a new const formatters from the log/mod.ts so we can use the formatter in a similar way to how we use handlers: log.formatters.jsonFormatter
• A ton of docs, please note that I've documented the following topics & quirks:
  • How to configure the logger to emit non-coloured json
  • How the first argument is always treated as the message and will be double encoded if not a string
  • How the emitted json looks based on different types of input
  • How to create a custom json formatter

[kt3k]

LGTM. Thanks!