是否可以在 for 循环中遍历长度属性的条件语句？答案

【问题标题】：Is it possible to iterate through a conditional statement for the length property in a for loop?是否可以在 for 循环中遍历长度属性的条件语句？
【发布时间】：2018-10-15 18:18:41
【问题描述】：

感谢您抽出宝贵时间查看此内容。代码如下。

let questions = [];

let Question = function(question, answers, number) {
    this.question = question;
    this.answers = answers;
    this.number = number;
}

let question1 = new Question('Is Javascript the best programming language?', 
['No', 'Yes'], 1);

let question2 = new Question('Is Javascript a web development language?', 
['No', 'Yes'], 1);

let question3 = new Question(`What is Javascript's official server side 
application called?`, ['BootStrap', 'Python', 'Node.js'], 2);

questions = [question1, question2, question3];

Question.randomQuestion = function() {
    let randomNum = Math.floor(Math.random() * 3);
    let randomQuestion = questions[randomNum];

    return randomQuestion;
}

Question.display = function(randomQuestion) {
    console.log(randomQuestion.question);
    debugger;
        // Why does the conditional give me undefined?
        for (let i = 0; i < questions[i].answers[i].length; i++)
        console.log(`${randomQuestion.answers[i]}`);    
    }

我想要做的是通过每次迭代获取 answers 属性的长度，但我得到一个错误： answers 是未定义的。为什么它是未定义的，有没有更好的方法呢？

【问题讨论】：

您将索引i 应用于问题数组和每个问题的answer 属性，这没有任何意义。
您介意详细说明一下吗？
questions[i].answers[i] 表示“第 i 个问题的第 i 个答案”。这真的是您想要的吗？您不应该用一个索引遍历问题，然后遍历每个问题都有另一个索引？
你的 for 循环应该像这样for (let i = 0; i < randomQuestion.answers[i].length; i++)
mm，你说得对，他需要第二个 for 循环来遍历问题，然后遍历答案

标签： javascript arrays object for-loop iteration

【解决方案1】：

有很多错误。基本上，当您遍历两个数组时，您需要两个循环。我用我的代码制作了这个 sn-p，希望对您有所帮助：

let questions = [];

let Question = function (question, answers, number) {
  this.question = question;
  this.answers = answers;
  this.number = number;
}

let question1 = new Question('Is Javascript the best programming language?',
  ['No', 'Yes'], 1);

let question2 = new Question('Is Javascript a web development language?',
  ['No', 'Yes'], 1);

let question3 = new Question(`What is Javascript's official server side 
application called?`, ['BootStrap', 'Python', 'Node.js'], 2);

questions = [question1, question2, question3];

const randomQuestion = function () {
  let randomNum = Math.floor(Math.random() * 3);
  let randomQuestion = questions[randomNum];
  return randomQuestion;
}

const display = function (randomQuestion) {
  const random_question = randomQuestion();
  console.log(random_question.question);
  //debugger;
  // Why does the conditional give me undefined?
  //dump all question and all answers
  for (let i = 0; i < questions.length; i++)
    for (let j = 0; j < questions[i].answers.length; j++)
      console.log(`${questions[i].answers[j]}`);
  //as an alternative :
  questions.forEach(e => {
    console.log(e.question);
    e.answers.forEach(a => {
      console.log(a)
    })
  })
}

display(randomQuestion);

【讨论】：