I have an Apex controller MyController which calls a VisualForce page via PageReference.

Here is my controller:

public with sharing class MyController {
    public String param1 { get; set; } // Define a property named param1
    public static String callVfPage() {
        String pageName = 'TimeZoneVFPage'; // Name of the Visualforce page
        String pageUrl = '/apex/' + pageName;

        PageReference pageRef = new PageReference(pageUrl);
        pageRef.getParameters().put('param1', 'value1'); // Set parameters if needed

        String pageContent = pageRef.getContent().toString();
        String processedValue = extractValueFromHtml(pageContent);
        return processedValue; // Return the extracted value
    private static String extractValueFromHtml(String htmlContent) {
        String processedValue = null;
        Integer startIndex = htmlContent.indexOf('<span id="processedValue">');
        Integer endIndex = htmlContent.indexOf('</span>', startIndex);
        if (startIndex != -1 && endIndex != -1) {
            processedValue = htmlContent.substring(startIndex + '<span id="processedValue">'.length(), endIndex);
        return processedValue;

And here is my VisualForce page:

<apex:page controller="MyController" showHeader="false" sidebar="false" 
           applyHtmlTag="false" applyBodyTag="false" standardStylesheets="false"
           docType="html-5.0" language="en-US" cache="true"
           contentType="text/html" title="TimeZoneVFPage" id="thePage"

    <apex:outputText value="{!param1}" id="param1" />
    <span id="processedValue">Old Value</span>

        window.onload = function() {
        function onPageLoad() {
            document.getElementById('processedValue').innerText = 'New Value';

When I call my controller method callVfPage using the execute anonymous window like this:

string output = MyController.callVfPage();

output is always "Old Value" instead of the expected "New Value". This page works fine when I preview it and displays New Value. But here, I think the script tag is not executed when I call it from Apex, therefore it returns "Old Value".

Any ideas on how I can make the Apex wait for the script to execute in my VisualForce page?

UPDATE: Here's what I am trying to do: I want to update each Account's timezone based on their Billing Address. Now I could easily use some sort of API and use a HTTP callout to get the timezone, but instead of making many API calls, I figured I could use a JS library to pass the figure out the timezone from the Billing Address, e.g using MomentJs.

Another possible solution could be to have a static list of timezones and countries/cities, and figure out the timezone based on the Billing Address that way, but then I would need to update this list manually.

  • This is an X-Y Problem. Running JavaScript code in Visualforce requires a browser environment, and Apex isn't a browser environment. In other words, what you're asking is impossible. There's nothing to wait for because the code would never run. You only get the emitted HTML source code for the page. Please edit your question to tell us what you're trying to do, and we'll help you with a solution.
    – sfdcfox
    Commented May 14 at 20:08
  • @sfdcfox please see my updated question.
    – ViqMontana
    Commented May 15 at 7:56

1 Answer 1


When you call PageReference.getContent() like this, it only loads the emitted HTML from Visualforce. You're not in a browser environment, so Apex can't run the JavaScript. You've already outlined two possible solutions, such as keeping a list of cities in records with their time zones, or making an API call. If you want to call a JavaScript library, you'll have to be a browser environment, such as by writing an Aura Component, a Lightning Web Component, a Visualforce page (which you can add directly to a page layout), a Flow, or something else.

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