Quick and dirty way to deep copy json objects in javascript (object prototypes are not copied)

deepCopy.js

function isNull(v) {
  return typeof v === "object" && !v;
}

function isPrimitive(v) {
  return ["number", "string", "boolean", "undefined"].indexOf(typeof v) !== -1 || isNull(v);
}

function isPlainObject(o) {
  return o && typeof o === "object" && o.constructor === Object;
}

function deepCopy(o) {
  var copy;

  if(Array.isArray(o)) {
    copy = [];

    for(var i = 0; i < o.length; i++) {
      if(isPrimitive(o[i])) {
        copy[i] = o[i];
      }
      else {
        copy[i] = deepCopy(o[i]);
      }
    }
    
    return copy;
  }
  else if(isPlainObject(o)) {
    copy = {};

    for(var p in o) {
      if(o.hasOwnProperty(p)) {
        if(isPrimitive(o[p])) {
          copy[p] = o[p];
        }
        else {
          copy[p] = deepCopy(o[p]);
        }
      }
    }

    return copy;
  }
  else {
    return o;
  }
}