code: function clonePureArray (subject, host) {
    var i = subject.length
    var start = host.length
  
    while (i --) {
      host[start + i] = subject[i]
    }
  
    return host
  }
docs: clone an object as a pure subject, and ignore non-number properties
  @param {Array} subject
  @param {Array|Object} host required, receiver which the subject be cloned to