Execute Custom JavaScript

from ironpdf import *

# Instantiate Renderer
renderer = ChromePdfRenderer()
 
# Example that change all to red style in JavaScript:
renderer.RenderingOptions.Javascript = "document.querySelectorAll('h1').forEach(function(el){el.style.color='red';})"

# Make sure to use the render options object that you created:
pdf = renderer.RenderHtmlAsPdf("<h1>Happy New Year!</h1>")
pdf.SaveAs("executed_js.pdf")

Execute Custom JavaScript

IronPDF for Python can inject and execute custom JavaScript against a page before it is rendered to PDF, giving you programmatic control over the HTML content at render time.

Getting Started

Assign a JavaScript string to RenderingOptions.Javascript on a ChromePdfRenderer instance. IronPDF will execute that script after the page has loaded and before the PDF is captured.

Understanding the Code

RenderingOptions.Javascript: A string containing JavaScript code that IronPDF injects and runs after the page finishes loading. In the example, this script selects all <h1> elements and sets their color to red using querySelectorAll and a forEach loop.
RenderHtmlAsPdf(html): Renders the HTML with the injected JavaScript applied. The resulting PDF reflects the DOM state after the script has run.

Use Cases

Injecting custom JavaScript at render time is useful for:

Hiding UI elements not relevant to a print view (navigation bars, sidebars, modals).
Applying dynamic styles based on conditions evaluated at render time.
Populating data into a page template before capturing it as a PDF.
Triggering print-specific layout changes without modifying the original HTML source.

Learn to convert HTML to PDF with IronPDF for Python!