Extend with JavaScript - Overview - Docs

JavaScript engine

The prebuilt PocketBase v0.17+ executable comes with embedded ES5 JavaScript engine (goja) which enables you to write custom server-side code using plain JavaScript.

You can start by creating *.pb.js file(s) inside a pb_hooks directory next to your executable.

// pb_hooks/main.pb.js

routerAdd("GET", "/hello/:name", (c) => {
    let name = c.pathParam("name")

    return c.json(200, { "message": "Hello " + name })
})

onModelAfterUpdate((e) => {
    console.log("user updated...", e.model.get("email"))
}, "users")

For convenience, when making changes to the files inside pb_hooks, the process will automatically restart/reload itself (currently supported only on UNIX based platforms). The *.pb.js files are loaded per their filename sort order.

For most parts, the JavaScript APIs are derived from Go with 2 main differences:

Go exported method and field names are converted to camelCase, for example:
app.Dao().FindRecordById("example", "RECORD_ID") becomes $app.dao().findRecordById("example", "RECORD_ID").
Errors are thrown as regular JavaScript exceptions and not returned as Go values.

Global objects

Below is a list with some of the commonly used global objects that are accessible from everywhere:

__hooks - The absolute path to the app pb_hooks directory.
$app - The current running PocketBase application instance.
$apis.* - API routing helpers and middlewares.
$os.* - OS level primitives (deleting directories, executing shell commands, etc.).
$security.* - Low level helpers for creating and parsing JWTs, random string generation, AES encryption, etc.
And many more - for all exposed APIs, please refer to the JSVM reference docs.

TypeScript declarations and code completion

While you can't use directly TypeScript (without transpiling it to JS on your own), PocketBase comes with builtin ambient TypeScript declarations that can help providing information and documentation about the available global variables, methods and arguments, code completion, etc. as long as your editor has TypeScript LSP support (most editors either have it builtin or available as plugin).

The types declarations are stored in pb_data/types.d.ts file. You can point to those declarations using the reference tripple-slash directive at the top of your JS file:

/// <reference path="../pb_data/types.d.ts" />

onAfterBootstrap((e) => {
    console.log("App initialized!")
})

If after referencing the types your editor still doesn't perform linting, then you can try to rename your file to have .pb.ts extension.

Caveats and limitations

Handlers scope

Each handler function (hook, route, middleware, etc.) is serialized and executed in its own isolated context as a separate "program". This means that you don't have access to custom variables and functions declared outside of the handler scope. For example, the below code will fail:

const name = "test"

onAfterBootstrap((e) => {
    console.log(name) // <-- name will be undefined inside the handler
})

The above serialization and isolation context is also the reason why error stack trace line numbers may not be accurate.

One possible workaround for sharing/reusing code across different handlers could be to move and export the reusable code portion as local module and load it with require() inside the handler but keep in mind that the loaded modules use a shared registry and mutations should be avoided when possible to prevent concurrency issues:

onAfterBootstrap((e) => {
    const config = require(`${__hooks}/config.js`)

    console.log(config.name)
})

Relative paths

Relative file paths are relative to the current working directory (CWD) and not to the pb_hooks.
To get an absolute path to the pb_hooks directory you can use the global __hooks variable.

Loading modules

Please note that the embedded JavaScript engine is not a Node.js or browser environment, meaning that modules that relies on APIs like window, fs, fetch, buffer or any other runtime specific API not part of the ES5 spec may not work!

You can load modules either by specifying their local filesystem path or by using their name, which will automatically search in:

the current working directory (affects also relative paths)
any node_modules directory
any parent node_modules directory, up to the closest package.json

Currently only CommonJS (CJS) modules are supported and can be loaded with const x = require(...).
ECMAScript modules (ESM) can be loaded by first precompiling and transforming your dependencies with a bundler like rollup, webpack, browserify, etc.

A common usage of local modules is for loading shared helpers or configuration parameters, for example:

// pb_hooks/utils.js
module.exports = {
    hello: (name) => {
        console.log("Hello " + name)
    }
}

// pb_hooks/main.pb.js
onAfterBootstrap((e) => {
    const utils = require(`${__hooks}/utils.js`)

    utils.hello("world")
})

Loaded modules use a shared registry and mutations should be avoided when possible to prevent concurrency issues.

Performance

The prebuilt executable comes with a prewarmed pool of 25 JS runtimes, which helps maintaining the handlers execution times on par with the Go equivalent code (see benchmarks). You can adjust the pool size manually with the --hooksPool=100 flag (increasing the pool size may improve the performance in high concurrent scenarios but also will increase the memory usage).

Note that the handlers performance may degrade if you have heavy computational tasks in pure JavaScript (eg. encryption, random generators, etc.). For such cases prefer using the exposed Go bindings (eg. $security.randomString(10)).

Engine limitations

We inherit some of the limitations and caveats of the embedded JavaScript engine (goja):

Has most of ES6 functionality already implemented but it is not fully spec compliant yet.
No concurrent execution inside a single handler (aka. no setTimeout/setInterval).
Wrapped Go structural types (such as maps, slices) comes with some peculiarities and do not behave the exact same way as native ECMAScript values (for more details see goja ToValue).
In relation to the above, DB json field values require the use of get() and set() helpers (this may change in the future).