SOURCE

function shadowCopy(a, b){
  if(!a || typeof a !== 'object'){
    return
  }
  if(!b || typeof b !== 'object'){
    return
  }
  for(var key in b){
    if(b.hasOwnProperty(key)){
      a[key] = b[key]
    }
  }
}

//var o = [1, 2, 3]
// defined new empty arr
//var newB = []
//shadowCopy(newB, o)
//console.log(newB)
//console.log(newB == o)

var o = {
  m: 1,
  n: {
    c: 2
  }
}
var newB = {}
shadowCopy(newB, o)
console.log(newB)
console.log(newB == o) // false