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Loading Javascript from a URL in Go with Net/HTTP

In this guide, we'll show you how to load custom javascript as a URL 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 javascript 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.

Moreover, adding a URL can be easier to do than passing the raw javascript content, as it allows you to later modify that javascript without having to modify the query made to PDFShift.

package main

import (

func main() {
    // You can get an API key at
    apiKey := "sk_xxxxxxxxxxxx"

    params := map[string]interface{}{
        "source": "",
        "javascript": ""

    // Marshal the parameters into JSON
    jsonParams, err := json.Marshal(params)
    if err != nil {
        fmt.Println("Error marshaling JSON:", err)

    // Create a new HTTP client
    client := &http.Client{}

    // Create a new request
    req, err := http.NewRequest("POST", "", bytes.NewBuffer(jsonParams))
    if err != nil {
        fmt.Println("Error creating request:", err)

    // Set request headers
    req.Header.Set("Content-Type", "application/json")

    // Set basic authentication header
    auth := "api:" + apiKey
    req.Header.Set("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(auth)))

    // Perform the request
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error performing request:", err)
    defer resp.Body.Close()

    // Read response body
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        fmt.Println("Error reading response body:", err)

    // Check response status code
    if resp.StatusCode >= 400 {
        fmt.Printf("Request failed with status code %d: %s\n", resp.StatusCode, string(body))

    // Save the PDF document
    err = ioutil.WriteFile("result.pdf", body, 0644)
    if err != nil {
        fmt.Println("Error saving PDF document:", err)

    fmt.Println("The PDF document was generated and saved to result.pdf")

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 javascript value to adjust the rendering of your page specifically when exporting the document to PDF.

For further details on the javascript property and its usage, please refer to our dedicated documentation.

We hope this guide was helpful. If you have any questions or noticed any issues on the code above,
feel free to drop us a line.