javascript - How to check if an object can be cloned by the structured clone algorithm - Stack Overflow

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The structured clone algorithm is a serialization algorithm used, among other things, to pass data between windows via window.postMessage. It supports recursive objects (unlike JSON) but not things like DOM Nodes, Functions, and Errors, and other

What I'd like is a simple way to check if a given object can be serialized by the structured clone algorithm. I could recursively walk the object and check if each property is a DOM Node, Function, or Error, but that's not a plete answer, and I was wondering if there was a better way.

The structured clone algorithm is a serialization algorithm used, among other things, to pass data between windows via window.postMessage. It supports recursive objects (unlike JSON) but not things like DOM Nodes, Functions, and Errors, and other

What I'd like is a simple way to check if a given object can be serialized by the structured clone algorithm. I could recursively walk the object and check if each property is a DOM Node, Function, or Error, but that's not a plete answer, and I was wondering if there was a better way.

• javascript
• structured-clone

Share Improve this question Follow asked Sep 19, 2015 at 21:42 RetsamRetsam 33.5k1111 gold badges7272 silver badges9494 bronze badges 3

• 5 Why not try, then catch the DATA_CLONE_ERR exception that it throws if it's not valid? If you catch an exception, the object is not serializable, otherwise it is. – Maximillian Laumeister Commented Sep 19, 2015 at 21:48
• 1 The API doesn't always use window.postMessage depending on the context, but for consistency I'd like it to report an error if the data isn't patible with the structured clone algorithm. – Retsam Commented Sep 19, 2015 at 22:20
• 1 Try/catch should work fine in that case too. – Maximillian Laumeister Commented Sep 19, 2015 at 22:23

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1 Answer 1

Sorted by: Reset to default 5

From the spec, I think it would be something like

function canBeCloned(val) {
  if(Object(val) !== val) // Primitive value
    return true;
  switch({}.toString.call(val).slice(8,-1)) { // Class
    case 'Boolean':     case 'Number':      case 'String':      case 'Date':
    case 'RegExp':      case 'Blob':        case 'FileList':
    case 'ImageData':   case 'ImageBitmap': case 'ArrayBuffer':
      return true;
    case 'Array':       case 'Object':
      return Object.keys(val).every(prop => canBeCloned(val[prop]));
    case 'Map':
      return [...val.keys()].every(canBeCloned)
          && [...val.values()].every(canBeCloned);
    case 'Set':
      return [...val.keys()].every(canBeCloned);
    default:
      return false;
  }
}

Note this has some limitations:

• I can't check if an object has a [[DataView]] internal slot
• {}.toString is not a reliable way to get the [[Class]], but is the only one.
• Other specifications may define how to clone additional kinds of objects

So it may be more reliable to attempt to run the algorithm, and see if it produces some error:

function canBeCloned(val) {
  try {
    window.postMessage(val,'*');
  } catch(err) {
    return false;
  }
  return true;
}

Note if you have a message event listener, it will be called. If you want to avoid this, send the value to another window. For example, you can create one using an iframe:

var canBeCloned = (function() {
  var iframe = document.createElement('iframe');
  document.body.appendChild(iframe);
  var win = iframe.contentWindow;
  document.body.removeChild(iframe);
  return function(val) {
    try { win.postMessage(val, '*'); }
    catch(err) { return false; }
    return true;
  };
})();

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