## Table of Contents

- [Return any value](#return-any-value)
- [Custom parameters](#custom-parameters)
  - [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)
- [Using npm packages](#using-npm-packages)
  - [Pin a version](#pin-a-version)
  - [Security restrictions](#security-restrictions)
- [When to add page](#when-to-add-page)
- [See also](#see-also)

---

[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)

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

\|

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

Your function runs remotely in a Node.js sandbox. The simplest function is just plain JavaScript — no browser, no page, no Puppeteer:

```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
```

When your function does not reference `page`, no browser is started. This makes execution faster and cheaper.

## Return any value

Functions can return strings, numbers, booleans, arrays, or plain objects:

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

const fn = microlink(() => ({

  greeting: 'Hello',

  items: [1, 2, 3],

  nested: { works: true }

}))

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

console.log(result.value)

// { greeting: 'Hello', items: [1, 2, 3], nested: { works: true } }
```

The return value is always available at `result.value`. If the function throws, `result.isFulfilled` is `false` and `result.value` contains the error details instead.

## Custom parameters

Any extra parameter you include in the request is forwarded to the function:

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

const greet = ({ name, greeting }) => `${greeting}, ${name}!`

const fn = microlink(greet)

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

  name: 'Kiko',

  greeting: 'Hello'

})

console.log(result.value) // 'Hello, Kiko!'
```

This is the simplest way to make one function reusable across different requests without changing the function code.

The following examples show how to use the Microlink API with CLI, cURL, JavaScript, Python, Ruby, PHP & Golang, targeting 'https://example.com' URL with 'function', 'greetings' & 'meta' API parameters:

### CLI Microlink API example

```bash
microlink https://example.com&function='({ greetings }) => greetings'&greetings='hello world'
```

### cURL Microlink API example

```bash
curl -G "https://api.microlink.io" \
  -d "url=https://example.com" \
  -d "function=(%7B%20greetings%20%7D)%20%3D%3E%20greetings" \
  -d "greetings=hello%20world" \
  -d "meta=false"
```

### JavaScript Microlink API example

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

const { data } = await mql('https://example.com', {
  function: "({ greetings }) => greetings",
  greetings: "hello world",
  meta: false
})
```

### Python Microlink API example

```python
import requests

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

querystring = {
    "url": "https://example.com",
    "function": "({ greetings }) => greetings",
    "greetings": "hello world",
    "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://example.com",
  function: "({ greetings }) => greetings",
  greetings: "hello world",
  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://example.com",
    "function" => "({ greetings }) => greetings",
    "greetings" => "hello world",
    "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://example.com")
    q.Set("function", "({ greetings }) => greetings")
    q.Set("greetings", "hello world")
    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://example.com', {

  function: "({ greetings }) => greetings",

  greetings: "hello world",

  meta: false

})
```

## Using npm packages

You can `require()` any npm package inside your function. Dependencies are detected automatically and installed on-the-fly:

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

const fn = microlink(() => {

  const { kebabCase } = require('lodash')

  return kebabCase('Hello World')

})

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

console.log(result.value) // 'hello-world'
```

When your function contains a `require()` call, the runtime:

1.  Parses your code to detect all dependency names.
2.  Installs them into an isolated sandbox during the install phase.
3.  Bundles everything during the build phase.
4.  Caches the result so subsequent runs with the same dependencies skip installation.

You can see how long each step takes in `result.profiling.phases`. A high install value on the first run is normal — it drops to zero once cached.

### Pin a version

Append the version to the package name:

```js
const cheerio = require('cheerio@1.0.0')
```

When no version is specified, the latest version is installed.

### Security restrictions

The runtime restricts certain system capabilities for security. Operations such as spawning child processes or writing to the filesystem outside the sandbox are not permitted. If a package tries to use a restricted capability, the function will return an error:

```json
{

  "isFulfilled": false,

  "value": {

    "name": "Error",

    "code": "ERR_ACCESS_DENIED",

    "permission": "ChildProcess",

    "message": "Access to this API has been restricted."

  }

}
```

## When to add page

When your function references `page`, Microlink starts a headless browser and navigates to the URL before calling your function. This gives you full Puppeteer access but takes more time:

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

const getTitle = ({ page }) => page.title()

const fn = microlink(getTitle)

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

console.log(result.value) // 'Example Domain'
```

If you only need to compute a value or call an external API, skip `page` entirely — your function will run faster.

See [Browser interaction](https://microlink.io/docs/guides/function/browser-interaction) for Puppeteer helpers, execution contexts, and browser automation.

## See also

- [Browser interaction](https://microlink.io/docs/guides/function/browser-interaction) — Puppeteer helpers and browser automation.
- [Profiling and performance](https://microlink.io/docs/guides/function/profiling-and-performance) — understand execution phases and optimization.
- [Function reference](https://microlink.io/docs/api/parameters/function) — response shape, plan limits, and compression.

Last updated on May 24, 2026

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