SOURCE

/**
 * 深度克隆方法
 */
function deepClone(source) {
  if (!source || typeof source !== 'object') {
    throw new Error('error arguments', 'shallowClone');
  }
  var targetObj = source.constructor === Array ? [] : {};
  for (var keys in source) {
    if (source.hasOwnProperty(keys)) {
      if (source[keys] && typeof source[keys] === 'object') {
        targetObj[keys] = source[keys].constructor === Array ? [] : {};
        targetObj[keys] = deepClone(source[keys]);
      } else {
        targetObj[keys] = source[keys];
      }
    }
  }
  return targetObj;
}

var a = {A: 1, B: 2}
var b = deepClone(a)
a.A = 3
console.log(a.A, b.A)