## Table of Contents

- [Function](#function)
- [Install](#install)
- [Your first function](#your-first-function)
  - [CLI Microlink API example](#cli-microlink-api-example)
  - [cURL Microlink API example](#curl-microlink-api-example)
  - [JavaScript Microlink API example](#javascript-microlink-api-example)
  - [Python Microlink API example](#python-microlink-api-example)
  - [Ruby Microlink API example](#ruby-microlink-api-example)
  - [PHP Microlink API example](#php-microlink-api-example)
  - [Golang Microlink API example](#golang-microlink-api-example)
- [Choose the lightest tool](#choose-the-lightest-tool)
- [What's next](#whats-next)

---

[API](https://microlink.io/docs/api/getting-started/overview)

[GUIDES](https://microlink.io/docs/guides) [MQL](https://microlink.io/docs/mql/getting-started/overview) [SDK](https://microlink.io/docs/sdk/getting-started/overview) [CARDS](https://microlink.io/docs/cards/getting-started/overview)

API GUIDES MQL SDK CARDS

Getting Started

[Overview](https://microlink.io/docs/guides)

[What is Microlink](https://microlink.io/docs/guides/what-is-microlink)

[Screenshot](https://microlink.io/docs/guides/screenshot)

[Customizing output](https://microlink.io/docs/guides/screenshot/customizing-output)

[Browser settings](https://microlink.io/docs/guides/screenshot/browser-settings)

[Page interaction](https://microlink.io/docs/guides/screenshot/page-interaction)

[Delivery and embedding](https://microlink.io/docs/guides/screenshot/embedding)

[Caching and performance](https://microlink.io/docs/guides/screenshot/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/screenshot/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/screenshot/troubleshooting)

[Data extraction](https://microlink.io/docs/guides/data-extraction)

[Defining rules](https://microlink.io/docs/guides/data-extraction/defining-rules)

[Page preparation](https://microlink.io/docs/guides/data-extraction/page-preparation)

[Delivery and response shaping](https://microlink.io/docs/guides/data-extraction/delivery-and-response)

[Caching and performance](https://microlink.io/docs/guides/data-extraction/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/data-extraction/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/data-extraction/troubleshooting)

[Embed](https://microlink.io/docs/guides/embed)

[SDK](https://microlink.io/docs/guides/embed/sdk)

[Iframe parameter](https://microlink.io/docs/guides/embed/iframe)

[Custom HTML/CSS](https://microlink.io/docs/guides/embed/metadata-api)

[Custom previews with AI](https://microlink.io/docs/guides/embed/custom-previews-with-ai)

[Caching and performance](https://microlink.io/docs/guides/embed/caching-and-performance)

[Private pages and proxy](https://microlink.io/docs/guides/embed/private-pages-and-proxy)

[Troubleshooting](https://microlink.io/docs/guides/embed/troubleshooting)

[Markdown](https://microlink.io/docs/guides/markdown)

[Choosing scope](https://microlink.io/docs/guides/markdown/choosing-scope)

[Delivery and response shaping](https://microlink.io/docs/guides/markdown/delivery-and-response)

[Function](https://microlink.io/docs/guides/function)

[Writing functions](https://microlink.io/docs/guides/function/writing-functions)

[Browser interaction](https://microlink.io/docs/guides/function/browser-interaction)

[Profiling and performance](https://microlink.io/docs/guides/function/profiling-and-performance)

[Troubleshooting](https://microlink.io/docs/guides/function/troubleshooting)

[PDF](https://microlink.io/docs/guides/pdf)

[Page size and layout](https://microlink.io/docs/guides/pdf/page-size-and-layout)

[Page preparation](https://microlink.io/docs/guides/pdf/page-preparation)

[Delivery and embedding](https://microlink.io/docs/guides/pdf/embedding)

[Caching and performance](https://microlink.io/docs/guides/pdf/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/pdf/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/pdf/troubleshooting)

[Metadata](https://microlink.io/docs/guides/metadata)

[Choosing fields](https://microlink.io/docs/guides/metadata/choosing-fields)

[Extending results](https://microlink.io/docs/guides/metadata/extending-results)

[Delivery and response shaping](https://microlink.io/docs/guides/metadata/delivery-and-response)

[Page preparation](https://microlink.io/docs/guides/metadata/page-preparation)

[Caching and performance](https://microlink.io/docs/guides/metadata/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/metadata/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/metadata/troubleshooting)

[Insights](https://microlink.io/docs/guides/insights)

[Technology detection](https://microlink.io/docs/guides/insights/technology-detection)

[Lighthouse reports](https://microlink.io/docs/guides/insights/lighthouse-reports)

[Caching and performance](https://microlink.io/docs/guides/insights/caching-and-performance)

[Troubleshooting](https://microlink.io/docs/guides/insights/troubleshooting)

[Common patterns](https://microlink.io/docs/guides/common/caching)

[Caching patterns](https://microlink.io/docs/guides/common/caching)

[Private pages](https://microlink.io/docs/guides/common/private-pages)

[Proxy](https://microlink.io/docs/guides/common/proxy)

[Troubleshooting](https://microlink.io/docs/guides/common/troubleshooting)

[Production patterns](https://microlink.io/docs/guides/common/production-patterns)

API GUIDES MQL SDK CARDS

Getting Started

[Overview](https://microlink.io/docs/guides)

[What is Microlink](https://microlink.io/docs/guides/what-is-microlink)

[Screenshot](https://microlink.io/docs/guides/screenshot)

[Customizing output](https://microlink.io/docs/guides/screenshot/customizing-output)

[Browser settings](https://microlink.io/docs/guides/screenshot/browser-settings)

[Page interaction](https://microlink.io/docs/guides/screenshot/page-interaction)

[Delivery and embedding](https://microlink.io/docs/guides/screenshot/embedding)

[Caching and performance](https://microlink.io/docs/guides/screenshot/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/screenshot/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/screenshot/troubleshooting)

[Data extraction](https://microlink.io/docs/guides/data-extraction)

[Defining rules](https://microlink.io/docs/guides/data-extraction/defining-rules)

[Page preparation](https://microlink.io/docs/guides/data-extraction/page-preparation)

[Delivery and response shaping](https://microlink.io/docs/guides/data-extraction/delivery-and-response)

[Caching and performance](https://microlink.io/docs/guides/data-extraction/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/data-extraction/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/data-extraction/troubleshooting)

[Embed](https://microlink.io/docs/guides/embed)

[SDK](https://microlink.io/docs/guides/embed/sdk)

[Iframe parameter](https://microlink.io/docs/guides/embed/iframe)

[Custom HTML/CSS](https://microlink.io/docs/guides/embed/metadata-api)

[Custom previews with AI](https://microlink.io/docs/guides/embed/custom-previews-with-ai)

[Caching and performance](https://microlink.io/docs/guides/embed/caching-and-performance)

[Private pages and proxy](https://microlink.io/docs/guides/embed/private-pages-and-proxy)

[Troubleshooting](https://microlink.io/docs/guides/embed/troubleshooting)

[Markdown](https://microlink.io/docs/guides/markdown)

[Choosing scope](https://microlink.io/docs/guides/markdown/choosing-scope)

[Delivery and response shaping](https://microlink.io/docs/guides/markdown/delivery-and-response)

[Function](https://microlink.io/docs/guides/function)

[Writing functions](https://microlink.io/docs/guides/function/writing-functions)

[Browser interaction](https://microlink.io/docs/guides/function/browser-interaction)

[Profiling and performance](https://microlink.io/docs/guides/function/profiling-and-performance)

[Troubleshooting](https://microlink.io/docs/guides/function/troubleshooting)

[PDF](https://microlink.io/docs/guides/pdf)

[Page size and layout](https://microlink.io/docs/guides/pdf/page-size-and-layout)

[Page preparation](https://microlink.io/docs/guides/pdf/page-preparation)

[Delivery and embedding](https://microlink.io/docs/guides/pdf/embedding)

[Caching and performance](https://microlink.io/docs/guides/pdf/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/pdf/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/pdf/troubleshooting)

[Metadata](https://microlink.io/docs/guides/metadata)

[Choosing fields](https://microlink.io/docs/guides/metadata/choosing-fields)

[Extending results](https://microlink.io/docs/guides/metadata/extending-results)

[Delivery and response shaping](https://microlink.io/docs/guides/metadata/delivery-and-response)

[Page preparation](https://microlink.io/docs/guides/metadata/page-preparation)

[Caching and performance](https://microlink.io/docs/guides/metadata/caching-and-performance)

[Private pages](https://microlink.io/docs/guides/metadata/private-pages)

[Troubleshooting](https://microlink.io/docs/guides/metadata/troubleshooting)

[Insights](https://microlink.io/docs/guides/insights)

[Technology detection](https://microlink.io/docs/guides/insights/technology-detection)

[Lighthouse reports](https://microlink.io/docs/guides/insights/lighthouse-reports)

[Caching and performance](https://microlink.io/docs/guides/insights/caching-and-performance)

[Troubleshooting](https://microlink.io/docs/guides/insights/troubleshooting)

[Common patterns](https://microlink.io/docs/guides/common/caching)

[Caching patterns](https://microlink.io/docs/guides/common/caching)

[Private pages](https://microlink.io/docs/guides/common/private-pages)

[Proxy](https://microlink.io/docs/guides/common/proxy)

[Troubleshooting](https://microlink.io/docs/guides/common/troubleshooting)

[Production patterns](https://microlink.io/docs/guides/common/production-patterns)

## Function

[Copy for LLM](https://microlink.io/docs/guides/function.md "Copy content for LLM")

\|

[View as Markdown](https://microlink.io/docs/guides/function.md "View content as Markdown")

The [function](https://microlink.io/docs/api/parameters/function) parameter lets you run any JavaScript remotely with full Puppeteer access, npm packages, and zero infrastructure to manage.

Send a function, get the result back. No Lambda bundle, no browser fleet, no server. Microlink handles the headless browser, installs dependencies on-the-fly, and executes your code in a sandboxed runtime.

## Install

The

[@microlink/function](https://www.npmjs.com/package/@microlink/function)

library lets you write normal JavaScript functions and run them remotely. It handles serialization, compression, and the API call for you:

```bash
npm install @microlink/function
```

## Your first function

Pass a JavaScript function and a target URL. The library sends it to the Microlink API and returns the result:

```js
const microlink = require('@microlink/function')

const fn = microlink(() => 40 + 2)

const result = await fn('https://example.com')

console.log(result.isFulfilled) // true

console.log(result.value) // 42
```

The function runs remotely. The result includes the returned value at `result.value` and execution metrics at `result.profiling`.

When your function references `page`, Microlink starts a headless browser and gives you full Puppeteer access:

The following examples show how to use the Microlink API with CLI, cURL, JavaScript, Python, Ruby, PHP & Golang, targeting 'https://developer.mozilla.org/en-US/docs/Web/API/Document/title' URL with 'function' & 'meta' API parameters:

### CLI Microlink API example

```bash
microlink https://developer.mozilla.org/en-US/docs/Web/API/Document/title&function='({ page }) => page.title()'
```

### cURL Microlink API example

```bash
curl -G "https://api.microlink.io" \
  -d "url=https://developer.mozilla.org/en-US/docs/Web/API/Document/title" \
  -d "function=(%7B%20page%20%7D)%20%3D%3E%20page.title()" \
  -d "meta=false"
```

### JavaScript Microlink API example

```javascript
import mql from '@microlink/mql'

const { data } = await mql('https://developer.mozilla.org/en-US/docs/Web/API/Document/title', {
  function: "({ page }) => page.title()",
  meta: false
})
```

### Python Microlink API example

```python
import requests

url = "https://api.microlink.io/"

querystring = {
    "url": "https://developer.mozilla.org/en-US/docs/Web/API/Document/title",
    "function": "({ page }) => page.title()",
    "meta": "false"
}

response = requests.get(url, params=querystring)

print(response.json())
```

### Ruby Microlink API example

```ruby
require 'uri'
require 'net/http'

base_url = "https://api.microlink.io/"

params = {
  url: "https://developer.mozilla.org/en-US/docs/Web/API/Document/title",
  function: "({ page }) => page.title()",
  meta: "false"
}

uri = URI(base_url)
uri.query = URI.encode_www_form(params)

http = Net::HTTP.new(uri.host, uri.port)
http.use_ssl = true

request = Net::HTTP::Get.new(uri)
response = http.request(request)

puts response.body
```

### PHP Microlink API example

```php
<?php

$baseUrl = "https://api.microlink.io/";

$params = [
    "url" => "https://developer.mozilla.org/en-US/docs/Web/API/Document/title",
    "function" => "({ page }) => page.title()",
    "meta" => "false"
];

$query = http_build_query($params);
$url = $baseUrl . '?' . $query;

$curl = curl_init();

curl_setopt_array($curl, [
    CURLOPT_URL => $url,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => "",
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => "GET"
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
    echo "cURL Error #: " . $err;
} else {
    echo $response;
}
```

### Golang Microlink API example

```
package main

import (
    "fmt"
    "net/http"
    "net/url"
    "io"
)

func main() {
    baseURL := "https://api.microlink.io"

    u, err := url.Parse(baseURL)
    if err != nil {
        panic(err)
    }
    q := u.Query()
    q.Set("url", "https://developer.mozilla.org/en-US/docs/Web/API/Document/title")
    q.Set("function", "({ page }) => page.title()")
    q.Set("meta", "false")
    u.RawQuery = q.Encode()

    req, err := http.NewRequest("GET", u.String(), nil)
    if err != nil {
        panic(err)
    }

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()

    body, err := io.ReadAll(resp.Body)
    if err != nil {
        panic(err)
    }

    fmt.Println(string(body))
}
```

```javascript
import mql from '@microlink/mql'

const { data } = await mql('https://developer.mozilla.org/en-US/docs/Web/API/Document/title', {

  function: "({ page }) => page.title()",

  meta: false

})
```

## Choose the lightest tool

Use [function](https://microlink.io/docs/api/parameters/function) when the built-in parameters stop being expressive enough, not as the default for every workflow.

| If you need                                                | Best option                                                                                                                                                                            | Why                                                                    |
| ---------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------- |
| Simple field extraction from the DOM                       | [data](https://microlink.io/docs/api/parameters/data)                                                                                                                                  | Declarative rules are shorter, easier to maintain, and easier to reuse |
| Inject CSS or JavaScript before another workflow           | [styles](https://microlink.io/docs/api/parameters/styles), [modules](https://microlink.io/docs/api/parameters/modules), or [scripts](https://microlink.io/docs/api/parameters/scripts) | Lighter than full browser automation                                   |
| Click, wait, compute, reshape, or orchestrate custom logic | [function](https://microlink.io/docs/api/parameters/function)                                                                                                                          | You get Puppeteer access plus any npm package                          |

For simpler extraction flows, start with [data extraction](https://microlink.io/docs/guides/data-extraction) and only escalate to [function](https://microlink.io/docs/api/parameters/function) when the declarative approach becomes limiting.

## What's next

- **[Writing functions](https://microlink.io/docs/guides/function/writing-functions)** — return values, custom parameters, and npm packages.
- **[Browser interaction](https://microlink.io/docs/guides/function/browser-interaction)** — Puppeteer helpers, execution contexts, and browser automation.
- **[Profiling and performance](https://microlink.io/docs/guides/function/profiling-and-performance)** — understand execution phases, plan limits, and optimization.
- **[Troubleshooting](https://microlink.io/docs/guides/function/troubleshooting)** — error handling, resource errors, and common failure modes.

Last updated on May 24, 2026

[Edit on GitHub](https://github.com/microlinkhq/www/blob/master/src/content/docs/guides/function/index.md)