code: function EaseElastic (opts) {
      EaseElastic.superclass.constructor.call(this, {action: opts.action})
  
      if (opts.period !== undefined) {
          this.period = opts.period
      }
  }
docs: @class
  Ease Elastic abstract class
  
  @memberOf cocos.actions
  @extends cocos.actions.ActionEase
  
  @opt {cocos.actions.ActionInterval} action
  @opt {Float} period