我試圖用JS實現“責任鏈模式”，但是我遇到的問題是，導出“chainController”后，所有外部調用都為NULL。從代碼來看，不存在異步問題，這讓我很困惑，請大家幫幫我，非常感謝代碼：/** Chain **/const Chain = function(handler) {  this.handler = handler;  this.nextHandler = null;}Chain.prototype.setNextHandler = function(nextHandler) {  this.nextHandler = nextHandler;  return nextHandler;}Chain.prototype.pass = function(...args) {  const result = this.handler(...args);  if (result === 'next') {    return this.nextHandler && this.nextHandler.pass(...args);  }  return result;}/** Handlers **/const equalTen = function(number) {  return (number === 10) ? 'equal-ten' : 'next';}const equalTwenty = function(number) {  return (number === 20) ? 'equal-twenty' : 'next';}const equalThirty = function(number) {  return (number === 30) ? 'equal-thirty' : 'next';}/** Controller **/const chainController = function(number) {  const checkEqualTen = new Chain(equalTen);  const checkEqualTwenty = new Chain(equalTwenty);  const checkEqualThirty = new Chain(equalThirty);  checkEqualTen    .setNextHandler(checkEqualTwenty)    .setNextHandler(checkEqualThirty);  return checkEqualTen.pass(number);};//is problem, when external call him, always get nulllet test = chainController(15);console.log(test);