@daldalso/logger

Fancy logging library using tagged template literal

Getting Started

1. yarn add @daldalso/logger
2. import { log } from "@daldalso/logger"
3. log("Hello, World!")

Full examples are shown in example.ts.

Usage

Log levels

There are 5 built-in log levels below, and you can directly call them to log something.

• log
• info
• success
• warning
• error

import { log, info, success, warning, error } from "@daldalso/logger";

log("Log");
info("Info");
success("Success");
warning("Warning");
error("Error");

Colors

There are 36 styles of decorating text and you can call col to use them.

import { col, log } from "@daldalso/logger";

log(col.red`Red`);
log(col.bgBlue`Blue`);

You can make a call chain to apply multiple styles.

import { col, log } from "@daldalso/logger";

log(col.italic.green`Italic and green`);
log("🚗💨 " + col.yellow.bgLBlack.underline`─────`);

Tagged template literal

The five functions can also be used as tagged template literals. In this case, expressions are handled depending on their type. For example, log(`Data: ${{ foo: 1 }}`); converts { foo: 1 } to a string and prints "Data: [object Object]", but log`Data: ${{ foo: 1 }}`; treats it as an object and prints:

When you want to print just an object without any template literals, call log(object) and it would be handled as its type.

Values

Most of object types are handled for better appearance.

import { log } from "@daldalso/logger";

log([ 1, 2, 3 ]);
log(new Map([ [ "foo", /bar/g ], [ log, true ] ]));
log(Promise.resolve("foo"));

[!IMPORTANT]

In a general way, retrieval of the state of Promises can't be synchronous. To bypass the limit, Logger calls Promise.race with Promise.resolve() to check the state, which means logging a Promise is asynchronous.

In the above example, switching the execution order of log(new Map(...)) and log(Promise.resolve("foo")) won't change the result.

Object with circular references is marked as below:

import { log } from "@daldalso/logger";

const circularObject = { foo: 1 };
circularObject.this = circularObject;
log(circularObject);

const circularArray = [ "bar" ];
circularArray.push(circularObject, circularArray);
log(circularArray);

Labeling

When you call Logger with multiple arguments, it labels each argument with numbers like below:

import { log } from "@daldalso/logger";

log("foo", "bar", "baz");

You can set the name of labels by calling any properties of its return value.

import { warning } from "@daldalso/logger";

warning("Loading is too long!").Task("Deleting redundant files")['⏱️']("100 seconds");

Styling

Logger's behavior can be configured by Logger.instance.setOptions. Actually, the above screenshots are not from the result of its default options, because the default options makes Logger print timestamps which are distracting for demonstration.

import { Logger, info, log } from "@daldalso/logger";

Logger.instance.setOptions({
  headings: {
    [LogLevel.VERBOSE]: col.black.bgLBlack`(LOG)`,
    [LogLevel.INFO]: col.black.bgCyan`(INF)`
  },
  headerFormat: col.lMagenta`[main]` + " $T $H "
});

log("Hello, World!");
info("How are you?");

Subscription

Logger calls console.log by default, but you can change this behavior with its subscription methods.

import { Logger, log } from "@daldalso/logger";

Logger.instance.removeSubscriber(1); // Removes default subscriber
Logger.instance.addSubscriber(
  (_, value) => console.error(value),
  { colored: true }
);
log("Hello, World!"); // This will be printed to stderr.

There are some functions that return a subscriber.

import { Logger, log, createDirectorySubscriber } from "@daldalso/logger";

Logger.instance.addSubscriber(
  createDirectorySubscriber("logs", { type: "time", interval: "daily" }),
  { colored: false } // Removes color data
);
log("Hello, World!"); // This will be printed to both stdout (by default) and a log file.

Instantiation

You can instantiate Logger to apply different configuration. Note that the instantiated Logger does not have any subscribers, which means you have to add one before logging with it.

import { Logger, createFileSubscriber } from "@daldalso/logger";

const fileLogger = new Logger({
  headerFormat: "$H "
});
fileLogger.addSubscriber(
  createFileSubscriber("example.log"),
  { colored: false }
);
fileLogger.verbose("Hello, World!"); // This won't be printed to stdout.