Question

When you check the Gmail’s client source code. There is VIEW_DATA variable holds many stuff related to user’s data. Is it possible to access this data via Javascript?

Answer 1

It looks like at some point after it’s used VIEW_DATA is reset to undefined, perhaps to save memory. Gmail seems to keep almost everything neatly tucked away in closures which makes getting to it from the global context difficult.

One possible—but fragile—approach would be to query the DOM for the <script> element where VIEW_DATA is defined, which would give you the original script, letting you eval() it in your own context. E.g.:

// get all of the <script> elements on the page
var scripts = document.getElementsByTagName( 'script' ),
    thisScript, varViewDataPos, viewDataScript, viewData
;

// loop through each one looking for VIEW_DATA being defined
for( var i = 0; i < scripts.length; i++ ) {
  thisScript = scripts[ i ].textContent;
  varViewDataPos = thisScript.indexOf( 'var VIEW_DATA=' );

  if( varViewDataPos >= 0 ) {
    // might as well toss everything before VIEW_DATA is defined
    viewDataScript = thisScript.slice( varViewDataPos );
    break;
  }
}

// eval what we found (if anything), but in a closure to avoid polluting
// the global namespace
viewData = ( function( script ) {
  eval( script );
  return VIEW_DATA;
} )( viewDataScript );

console.log( viewData || 'Oops, script not found.' );

Like I said, though, like any screen-scraping this is pretty fragile. If Google moves anything around you may find yourself suddenly eval-ing things you don’t want to, like function calls that will end up breaking the page. Use it at your own risk.

You may find find that ultimately other methods, like trying to find the data you’re looking for in the DOM instead, are more sensible.