clone.js

function clone(thing, opts) {
  var newObject = {};
  if (thing instanceof Array) {
    return thing.map(function (i) { return clone(i, opts); });
  } else if (thing instanceof Date) {
    return new Date(thing);
  } else if (thing instanceof RegExp) {
    return new RegExp(thing);
  } else if (thing instanceof Function) {
    return opts && opts.newFns ? new Function('return ' + thing.toString())() : thing;
  } else if (thing instanceof Object) {
    Object.keys(thing).forEach(function (key) { newObject[key] = clone(thing[key], opts); });
    return newObject;
  } else if ([ undefined, null ].indexOf(thing) > -1) {
    return thing;
  } else {
    if (thing.constructor.name === 'Symbol') {
      return Symbol(thing.toString().replace(/^Symbol\(/, '').slice(0, -1));
    }
    return thing.__proto__.constructor(thing);
  }
}

var a = {
  a: undefined,
  b: null,
  c: 'a',
  d: 0,
  e: Symbol('a'),
  f: {},
  g: { a:1 },
  h: [],
  i: [ { a:2 }, { a:3 } ],
  j: [ 1, 2 ],
  k: function (a) { return a; },
  l: /[a-z]/g,
  z: [ {
    a: undefined,
    b: null,
    c: 'b',
    d: 1,
    e: Symbol(1),
    f: {},
    g: { b:2 },
    h: { c:{ c:3 } },
    i: { a:Symbol('b') },
    j: { a:undefined, b:null },
    k: [],
    l: [ 1, [ 1, 2 ], [ [ 1, 2, 3 ] ] ],
    m: function (a) { return !a; },
    n: { a:function (a) { return !!a; } },
    o: /(a|b)/i
     } ]
};
var b = clone(a);
var c = clone(a, { newFns:true });


/* Results - value beneath each for reference:

a.a === b.a --> true
undefined

a.b === b.b --> true
null

a.c === b.c --> true
'a'

a.d === b.d --> true
0

a.e === b.e --> false
Symbol(a)

a.f === b.f --> false
{}

a.g === b.g --> false
{ a:1 }

a.h === b.h --> false
[]

a.i === b.i --> false
[ { a:2 }, { a:3 } ]

a.i[0] === b.i[0] --> false
{ a:2 }

a.i[0].a === b.i[0].a --> true
2

a.j === b.j --> false
[ 1, 2 ]

a.k === b.k --> true
a.k === c.k --> false
function (a) { return a; }

a.l === b.l --> false
/[a-z]/g

a.z === b.z --> false
[Object]

a.z[0].a === b.z[0].a --> true
undefined

a.z[0].b === b.z[0].b --> true
null

a.z[0].c === b.z[0].c --> true
'b'

a.z[0].d === b.z[0].d --> true
1

a.z[0].e === b.z[0].e --> 
false
Symbol(1)

a.z[0].f === b.z[0].f --> false
{}

a.z[0].g === b.z[0].g -- > false
{ b:2 }

a.z[0].g.b === b.z[0].g.b --> true
2

a.z[0].h === b.z[0].h --> false
{ c:{ c:3 } }

a.z[0].h.c === b.z[0].h.c --> false
{ c:3 }

a.z[0].h.c.c === b.z[0].h.c.c --> true
3

a.z[0].i === b.z[0].i --> false
{ a:Symbol(b) }

a.z[0].i.a === b.z[0].i.a --> false
Symbol(b)

a.z[0].j === b.z[0].j --> false
{ a:undefined, b:null }

a.z[0].j.a === b.z[0].j.a --> true
undefined

a.z[0].k === b.z[0].k --> false
[]

a.z[0].l === b.z[0].l --> false
[ 1, [ 1, 2 ], [ [ 1, 2, 3 ] ] ]

a.z[0].l[1] === b.z[0].l[1] --> false
[ 1, 2 ]

a.z[0].l[1][1] === b.z[0].l[1][1] --> true
2

a.z[0].m === b.z[0].m --> true
a.z[0].m === c.z[0].m --> false
function (a) { return !a; }

a.z[0].n === b.z[0].n --> false
{ a:function (a) { return !!a; } }

a.z[0].n.a === b.z[0].n.a --> true
a.z[0].n.a === c.z[0].n.a --> false
function (a) { return !!a; }

a.z[0].o === b.z[0].o --> false
/(a|b)/i

*/