---
title: "Loading Javascript from a string"
description: "Follow this guide to learn how to add custom javascript to your page to customize the output of your generated PDF. This allows you to modify elements on the page, add or remove content, etc. This guide uses PHP and the Guzzle library and relies on the PDFShift's API."
language: 'PHP'
library: 'Guzzle'
property: 'javascript'
output: 'pdf'
related: ['adding-a-custom-header-or-footer', 'loading-css-from-a-string', 'loading-css-from-a-url', 'loading-javascript-from-a-url']
default: false
---

In this guide, we'll show you how to load custom javascript code as a given string when converting an HTML document to PDF using PDFShift's API. This allows you to add custom JS to your page to customize the output of your generated PDF.

It can be interesting to be able to set a custom JS value to adjust the rendering of your page specifically when exporting the document to PDF.
This allows you to keep a standard look and feel to your users, but adjust some areas when sending that same document to PDFShift to get back a PDF.

```php
use GuzzleHttp\Client;
use GuzzleHttp\Exception\RequestException;

# You can get an API key at https://pdfshift.io
$api_key = 'sk_xxxxxxxxxxxx'

$params = array (
    'source' => 'https://www.example.com',
    'javascript' => 'document.querySelector("h1").style.color = "red";'
)

// Create a Guzzle client
$client = new Client();
try {
    // Make the POST request
    $response = $client->post('https://api.pdfshift.io/v3/convert/pdf', [
        'headers' => [
            'Content-Type' => 'application/json',
            'X-API-Key' => $api_key
        ],
        'json' => $params
    ]);

    // Get the response body
    $body = $response->getBody()->getContents();

    // Save the file to result.pdf
    file_put_contents('result.pdf', $body);

    echo 'The PDF document was generated and saved to result.pdf';
} catch (RequestException $e) {
    if ($e->hasResponse()) {
        $statusCode = $e->getResponse()->getStatusCode();
        $reasonPhrase = $e->getResponse()->getReasonPhrase();
        throw new Exception("Request failed with status code $statusCode: $reasonPhrase");
    } else {
        throw new Exception("Request failed: " . $e->getMessage());
    }
}
```

The `javascript` parameter accepts either a string or a URL. It will be used as the javascript for the page when converting it to PDF. This allows you to set a custom JS value to adjust the rendering of your page specifically when exporting the document to PDF.