how to fetch web page source code with javascript

var myLoc = window.prompt('Please enter a web site address', 'http://');
getHttp =   myLoc.substring(0, 7);
 
if ( getHttp == "http://")
{
finalUrl = myLoc;
} else {
finalUrl = 'http://' + myLoc;
}
 
window.location = 'view-source:' + finalUrl;