The solution from @inaspin works well. However, sometimes web pages contain tons of scripts that are not needed for text web scraping. Here is an extended executeScript command that removes scripts from the returned HTML code:
{
"Command": "executeScript",
"Target": "var str = document.body.innerHTML; // Get page source\n\n//Next: Clean up HTML source before further processing \n\n//First remove scripts and style tags with their content\nstr = str.replace(/<script\\b[^<]*(?:(?!<\\/script>)<[^<]*)*<\\/script>/gi, '');\nstr = str.replace(/<style\\b[^<]*(?:(?!<\\/style>)<[^<]*)*<\\/style>/gi, '');\n \n//Then remove all remaining tags but keep their content\nstr = str.replace(/<[^>]+>/g, '');\n \n//Clean up whitespace\nstr = str.replace(/\\s+/g, ' ').trim();\n \nreturn str;",
"Value": "html",
"Description": "Extract HTML code of website. Remove scripts."
}