javascript - 不使用 .join() 连接数组中的项目列表

Question

我试图弄清楚如何返回一个句子，其中我有一个项目列表，并且必须用“，”分隔它们。但是，如果数组仅包含一个项目，您将只返回不带逗号的单词，如果有两个单词，则您将在第一个单词之后返回一个逗号，而不是最后一个单词。

var conceptList = ['apple', 'orange', 'banana'];
var concepts = joinList(conceptList);

function joinList() {

  for (var i = 0; i < conceptList.length; i++) {
    if (conceptList.length) {
      conceptList[i];
    }  
  return conceptList;
  }
}

console.log("Today I learned about " + concepts + ".");

Answer 1

简单的方法是将每个元素附加到字符串中，后跟 ', '，然后在返回字符串之前删除尾随的 ', '。

/*
* Write a loop that joins the contents of conceptList together
* into one String, concepts, with each list item separated from
* the previous by a comma.
*
* Note: you may not use the built-in Array join function.
*/

var conceptList = ['apple', 'orange', 'banana'];
// a custom function written by you (you must define it too!)
var concepts = joinList(conceptList);

function joinList() {
  var str = '';
  for (var i = 0; i < conceptList.length; i++) {
    str += conceptList[i] + ', ';
  }
  
  return str.substr(0, str.length-2);
}

console.log("Today I learned about " + concepts + ".");