Question: What is the most efficient way to clone a JavaScript object? I've seen `obj = eval(uneval(o));` being used, but [that's non-standard and only supported by Firefox](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/uneval).  

 I've done things like `obj = JSON.parse(JSON.stringify(o));` but question the efficiency.   

 I've also seen recursive copying functions with various flaws.

I'm surprised no canonical solution exists.

Answer: 
```
// obj target object, vals source object
var setVals = function (obj, vals) {
    if (obj && vals) {
        for (var x in vals) {
            if (vals.hasOwnProperty(x)) {
                if (obj[x] && typeof vals[x] === 'object') {
                    obj[x] = setVals(obj[x], vals[x]);
                } else {
                    obj[x] = vals[x];
                }
            }
        }
    }
    return obj;
};

```
Single-line ECMAScript 6 solution (special object types like Date/Regex not handled):

```js
const clone = (o) =>
  typeof o === 'object' && o !== null ?      // only clone objects
  (Array.isArray(o) ?                        // if cloning an array
    o.map(e => clone(e)) :                   // clone each of its elements
    Object.keys(o).reduce(                   // otherwise reduce every key in the object
      (r, k) => (r[k] = clone(o[k]), r), {}  // and save its cloned value into a new object
    )
  ) :
  o;                                         // return non-objects as is

var x = {
  nested: {
    name: 'test'
  }
};

var y = clone(x);

console.log(x.nested !== y.nested);
```