Copy JS object in ES5 way

copyObject.js

// http://speakingjs.com/es5/ch17.html#code_copyOwnPropertiesFrom

// To create an identical copy of an object, you need to get two things right:
// - The copy must have the same prototype as the original.
// - The copy must have the same properties, with the same attributes as the original.


function copyObject(orig, deep) {
    // 1. copy has same prototype as orig
    var copy = Object.create(Object.getPrototypeOf(orig));

    // 2. copy has all of orig’s properties
    copyOwnPropertiesFrom(copy, orig, deep);

    return copy;
}

function copyOwnPropertiesFrom(target, source, deep) {
    Object.getOwnPropertyNames(source)  
    .forEach(function(propKey) {  
        var desc = Object.getOwnPropertyDescriptor(source, propKey);
        Object.defineProperty(target, propKey, desc);
        if (deep && typeof desc.value === 'object') {
          target[propKey] = copyObject(source[propKey], deep);
        }
    });
    return target;
}

I added this sanity check:

        if (!orig || !orig.prototype) {
            return orig;
        }

Otherwise getPrototypeOf will fail, and the input was not always guaranteed to be an object.