JavaScript

Example
It's very easy to start sending logs to Logtail:
const { Logtail } = require("@logtail/node");
​
const logtail = new Logtail("<source-token>");
​
logtail.info("logtail integration is ready");
logtail.warn("log structured data", {
    item: {
        url: "https://fictional-store.com/item-123",
        price: 100.00
    }
});
As a result, the following JSON rows will be ingested:
{
    "dt": "2021-03-29T11:24:54.788Z",
    "level": "info",
    "message": "logtail integration is ready"
}
​
{
    "dt": "2021-03-29T11:24:54.788Z",
    "level": "warn",
    "message": "log structured data",
    "item": {
        "url": "https://fictional-store.com/item-123",
        "price": 100.00
    }
}
Installation
Node.js
Frontend (NPM)
Frontend (UMD)
Simply install the library from NPM:
npm install @logtail/node
Then you can require it or import in your codebase:
// start by loading the Logtail class
const { Logtail } = require("@logtail/node");
​
// ... or if you're using ES modules:
import { Logtail } from "@logtail/node";
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:
// in your backend code:
const { Node: Logtail } = require("@logtail/js");
​
// in your frontend code:
import { Browser as Logtail } from "@logtail/js";
​
You can simply install the library from NPM:
npm install @logtail/browser
... and import it into your JavaScript code as you're used to:
import { Logtail } from "@logtail/browser";
You can use the UMD build directly from a CDN:
<script src="https://unpkg.com/browse/@logtail/[email protected]/dist/umd/logtail.js"></script>
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:
const Koa = require("koa");
const { Logtail } = require("@logtail/koa");
​
// Create a new Koa instance
const koa = new Koa();
​
// Create a new Logtail client
const logtail = new Logtail("logtail-source-token");
​
// Attach Koa to enable HTTP request logging
logtail.attach(koa);
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:
const winston = require("winston");
const { Logtail } = require("@logtail/node");
const { LogtailTransport } = require("@logtail/winston");
​
// Create a Logtail client
const logtail = new Logtail("logtail-source-token");
​
// Create a Winston logger - passing in the Logtail transport
const logger = winston.createLogger({
  transports: [new LogtailTransport(logtail)],
});
​
// Log as normal in Winston - your logs will sync with Logtail.com!
logger.log({
  level: "info", // <-- will use Logtail's `info` log level,
  message: "Some message", // <-- will also be passed to Logtail
});
Install the @logtail/bunyan NPM package and set up the Logtail stream according to the following example:
const bunyan = requrie("bunyan");
const { Logtail } = require("@logtail/node");
const { LogtailStream } = require("@logtail/bunyan");
​
// Create a Logtail client
const logtail = new Logtail("logtail-source-token");
​
// Create a Bunyan logger - passing in the Logtail stream
const logger = bunyan.createLogger({
  name: "Example logger",
  level: "debug",
  streams: [
    {
      stream: new LogtailStream(logtail),
    },
  ],
});
​
// Log as normal in Bunyan - your logs will be sent to Logtail.com
logger.info("Hello from Bunyan");
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:
const logtail = new Logtail("<your-source-token>");
​
logtail.info("simple log message");
logtail.warn("warning with additional information", {
    resource: {
        type: "store-item",
        id: 123456,
        inStock: false
    }
});
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:
import { LogLevel } from "@logtail/types";
// note: you don't need to install any additional packages
​
logtail.log("this is important", LogLevel.Error);
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:
async function enrichLogs(log) {
    return {
        ...log,
        userId: getCurrentUserId()
    };
}
​
logtail.use(enrichLogs);
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:
import { ILogtailLog } from "@logtail/types";
​
async function enrichLogs(log: ILogtailLog): Promise<ILogtailLog> {
    return {
        ...log,
        userId: getCurrentUserId()
    };
}

Getting started

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