Posted on Aug 26 • Originally published at thinkthroo.com

logger.ts in Motia.dev codebase.

In this article, we review logger.ts in Motia.dev codebase. We will look at:

logger class
prettyPrint function
colors.js package

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logger class

You will find the following code in packages/core/src/logger.ts.

export class Logger { /** * Why do we need two level of listeners? * * Core listeners pass along to children loggers. * * However, base listeners do not pass along to children loggers. * Those are specific to each logger in the hierarchy. */ private readonly listeners: LogListener[] = [] constructor( readonly isVerbose: boolean = false, private readonly meta: Record<string, unknown> = {}, private readonly coreListeners: LogListener[] = [], ) {} child(meta: Record<string, unknown>): Logger { return new Logger(this.isVerbose, { ...this.meta, ...meta }, this.coreListeners) } // eslint-disable-next-line @typescript-eslint/no-explicit-any private _log(level: string, msg: string, args?: any) { const time = Date.now() const meta = { ...this.meta, ...(args ?? {}) } prettyPrint({ level, time, msg, ...meta }, !this.isVerbose) this.coreListeners.forEach((listener) => listener(level, msg, meta)) this.listeners.forEach((listener) => listener(level, msg, meta)) } info(message: string, args?: unknown) { if (isInfoEnabled) { this._log('info', message, args) } } error(message: string, args?: unknown) { this._log('error', message, args) } debug(message: string, args?: unknown) { if (isDebugEnabled) { this._log('debug', message, args) } } warn(message: string, args?: unknown) { if (isWarnEnabled) { this._log('warn', message, args) } } // eslint-disable-next-line @typescript-eslint/no-explicit-any log(args: any) { this._log('info', args.msg, args) } addListener(listener: LogListener) { this.listeners.push(listener) } } export const globalLogger = new Logger()

_log function is reused and accepts parameters as shown below:

private _log(level: string, msg: string, args?: any) {

Here, depending on the level, prettyPrint function applies a color to a text.

prettyPrint function

You will find prettyPrint function in packages/core/src/pretty-print.ts and it is defined as shown below:

// eslint-disable-next-line @typescript-eslint/no-explicit-any export const prettyPrint = (json: Record<string, any>, excludeDetails = false): void => { // eslint-disable-next-line @typescript-eslint/no-unused-vars const { time, traceId, msg, flows, level, step, ...details } = json const levelTag = levelTags[level] const timestamp = timestampTag(`[${new Date(time).toLocaleTimeString()}]`) const objectHasKeys = Object.keys(details).length > 0 console.log(`${timestamp} ${traceIdTag(traceId)} ${levelTag} ${stepTag(step)} ${msg}`) if (objectHasKeys && !excludeDetails) { console.log(prettyPrintObject(details)) } }

Here, levelTag is assigned a value based on level as shown below:

const levelTag = levelTags[level]

levelTags is defined at line #7 in pretty-print.ts as shown below:

const levelTags: Record<string, string> = { error: colors.red('[ERROR]'), info: colors.blue('[INFO]'), warn: colors.yellow('[WARN]'), debug: colors.gray('[DEBUG]'), trace: colors.gray('[TRACE]'), }

colors.js package

get color and style in your node.js console

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Usage

By popular demand, colors now ships with two types of usages!

The super nifty way

var colors = require('colors'); console.log('hello'.green); // outputs green text console.log('i like cake and pies'.underline.red) // outputs red underlined text console.log('inverse the color'.inverse); // inverses the color console.log('OMG Rainbows!'.rainbow); // rainbow console.log('Run the trap'.trap); // Drops the bass

2. or a slightly less nifty way which doesn’t extend String.prototype

var colors = require('colors/safe'); console.log(colors.green('hello')); // outputs green text console.log(colors.red.underline('i like cake and pies')) // outputs red underlined text console.log(colors.inverse('inverse the color')); // inverses the color console.log(colors.rainbow('OMG Rainbows!')); // rainbow console.log(colors.trap('Run the trap')); // Drops the bass