Node.js使用“责任链模式”，但导出后，所有外部调用都是空的

Question

我试图用JS实现“责任链模式”，但是我遇到的问题是，导出“chainController”后，所有外部调用都为NULL。从代码来看，不存在异步问题，这让我很困惑，请大家帮帮我，非常感谢代码：/** 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);

Answer 1

发生这种情况是因为您从链中的最后一个调用 next (checkEqualThirty()) - 但没有下一个，因此默认答案分配为nextHandler-null因此null返回并 console.logged。

你已经没有给自己留下退路了。我修改了代码，以便您在 pass 方法中容纳其他可能性。

/** 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) {

  let result = this.handler(...args);

  if (result === 'next' && this.nextHandler !== null) {

    result = this.nextHandler.pass(...args);

  } else if (result === 'next') {

    result = "Not found";

  }

  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 null

console.log(chainController(5));

console.log(chainController(10));

console.log(chainController(15));

console.log(chainController(20));

console.log(chainController(25));

console.log(chainController(30));

console.log(chainController(35));