JavaScript

Example
It's very easy to start sending logs to Logtail:
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const { Logtail } = require("@logtail/node");
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​
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const logtail = new Logtail("<source-token>");
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​
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logtail.info("logtail integration is ready");
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logtail.warn("log structured data", {
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    item: {
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        url: "https://fictional-store.com/item-123",
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        price: 100.00
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    }
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});
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As a result, the following JSON rows will be ingested:
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{
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    "dt": "2021-03-29T11:24:54.788Z",
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    "level": "info",
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    "message": "logtail integration is ready"
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}
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​
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{
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    "dt": "2021-03-29T11:24:54.788Z",
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    "level": "warn",
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    "message": "log structured data",
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    "item": {
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        "url": "https://fictional-store.com/item-123",
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        "price": 100.00
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    }
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}
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Installation
Node.js
Frontend (NPM)
Frontend (UMD)
Simply install the library from NPM:
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npm install @logtail/node
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Then you can require it or import in your codebase:
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// start by loading the Logtail class
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const { Logtail } = require("@logtail/node");
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​
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// ... or if you're using ES modules:
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import { Logtail } from "@logtail/node";
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If your project contains both Node.js and frontend code, you can use our universal package @logtail/js which combines the node and browser packages:
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// in your backend code:
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const { Node: Logtail } = require("@logtail/js");
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​
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// in your frontend code:
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import { Browser as Logtail } from "@logtail/js";
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​
You can simply install the library from NPM:
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npm install @logtail/browser
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... and import it into your JavaScript code as you're used to:
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import { Logtail } from "@logtail/browser";
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You can use the UMD build directly from a CDN:
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<script src="https://unpkg.com/browse/@logtail/[email protected]/dist/umd/logtail.js"></script>
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Integrations
We provide integrations with several existing frameworks and logging solutions.
Koa
Winston
Bunyan
Install the following @logtail/koa NPM package and then attach the Logtail instance as a middleware to your Koa instance:
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const Koa = require("koa");
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const { Logtail } = require("@logtail/koa");
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​
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// Create a new Koa instance
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const koa = new Koa();
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​
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// Create a new Logtail client
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const logtail = new Logtail("logtail-source-token");
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​
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// Attach Koa to enable HTTP request logging
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logtail.attach(koa);
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How the middleware works
Successful requests
A successful request is one that returns a non-4xx or 5xx status code, and doesn't throw any uncaught errors while handling the requests. These are logged to Logtail using LogLevel.Info​
4xx status codes
These are not considered errors but warnings and log with the same message using LogLevel.Warn​
5xx status codes
Responses that contain a 5xx status code are considered errors and are logged with LogLevel.Error​
Additional logging
Since this Koa plugin extends the regular @logtail/node logger, you can use the .log|info|warn|error functions as normal to handle logging anywhere in your app.
Install the @logtail/winston NPM package and set up the Logtail transport according to the following example:
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const winston = require("winston");
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const { Logtail } = require("@logtail/node");
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const { LogtailTransport } = require("@logtail/winston");
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​
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// Create a Logtail client
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const logtail = new Logtail("logtail-source-token");
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​
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// Create a Winston logger - passing in the Logtail transport
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const logger = winston.createLogger({
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  transports: [new LogtailTransport(logtail)],
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});
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​
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// Log as normal in Winston - your logs will sync with Logtail.com!
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logger.log({
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  level: "info", // <-- will use Logtail's `info` log level,
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  message: "Some message", // <-- will also be passed to Logtail
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});
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Install the @logtail/bunyan NPM package and set up the Logtail stream according to the following example:
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const bunyan = requrie("bunyan");
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const { Logtail } = require("@logtail/node");
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const { LogtailStream } = require("@logtail/bunyan");
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​
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// Create a Logtail client
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const logtail = new Logtail("logtail-source-token");
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​
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// Create a Bunyan logger - passing in the Logtail stream
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const logger = bunyan.createLogger({
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  name: "Example logger",
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  level: "debug",
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  streams: [
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    {
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      stream: new LogtailStream(logtail),
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    },
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  ],
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});
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​
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// Log as normal in Bunyan - your logs will be sent to Logtail.com
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logger.info("Hello from Bunyan");
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Usage
Setting up the integration is very easy. All you need is a source-token that you'll get after you create a Source in your logtail.com account. With the source token at hand, you can create a Logtail instance and start logging:
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const logtail = new Logtail("<your-source-token>");
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​
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logtail.info("simple log message");
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logtail.warn("warning with additional information", {
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    resource: {
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        type: "store-item",
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        id: 123456,
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        inStock: false
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    }
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});
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The first argument is either a string message or an instance of Error. The second argument is an optional object, which can contain a tree structure with string, numeric, boolean, and Date values.
There are four levels of log messages: debug, info, warn,  and error. You can either log by calling the respective functions on the Logtail object, or you can pass the level as an additional parameter to the generic log function:
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import { LogLevel } from "@logtail/types";
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// note: you don't need to install any additional packages
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​
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logtail.log("this is important", LogLevel.Error);
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Middleware
You can intercept every logged item and modify it before it's pushed to Logtail. This could be useful for example for adding the current user's ID to the log:
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async function enrichLogs(log) {
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    return {
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        ...log,
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        userId: getCurrentUserId()
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    };
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}
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​
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logtail.use(enrichLogs);
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TypeScript support
If you're using Logtail in a TypeScript codebase, you can take advantage of our types. The custom middleware function from the previous example could look like this:
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import { ILogtailLog } from "@logtail/types";
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​
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async function enrichLogs(log: ILogtailLog): Promise<ILogtailLog> {
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    return {
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        ...log,
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        userId: getCurrentUserId()
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    };
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}
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Getting started
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Python
Last modified 7mo ago
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