javascript - For 语句循环遍历数组和数组项到基于模式识别追加匹配的新数组

Question

我没有从该函数中得到预期的结果。我期望的是我将有四个数组，其中包含多个项目。但相反，我对控制台中的所有内容都未定义。以下是我对该功能的说明:

Your job is to loop over this array and put items with similarities into four brand new arrays using regular expressions and the Array.push() method:

• one named og for items that end with og and are 3 letters long or less
• one named at for items that end with at that are longer than 3 letters
• one named numberFirst for items that start with numbers
• one named numberLast for items that end with numbers

对于我的 if 和 else if 语句，我让它们测试该项目是否与我在顶部创建的表达式匹配。如果匹配，则评估为 true。我认为要么是我的 if 语句错误，要么是我为模式识别创建正则表达式的方式错误。

var mainList = ['catalog', 'dog', 'cat', 'hog', 'muskrat', 'World War 3', 'blog', 'frog', '25th of March', 'bat', 'log', 'March 25', 'slog', '10 Downing street', 'flat', 'fat', 'splat', 'blat', 'frat', 'rat', '23 Skidoo', 'Catch 22', '10 4 Good Buddy', 'fog'];
var re = /$og/; //one named 'og' for items that end with 'og' and are 3 letters long or less//
var re2 = /$at/; //one named 'at' for items that end with 'at' that are longer than 3 letters//
var re3 = /[^0-9]/; //one named 'numberFirst' for items that start with numbers//
var re4 = /$[0-9]/; //one named 'numberLast' for items that end with numbers
var arrayOG = [];
var arrayAT = [];
var arrayNumberFirst = [];
var arrayNumberLast = [];

function loop(item) {
  for (var i = 0; i < mainList.length; i++) {
    if (re.test(item) == true && item.length <= 3) {
      arrayOG.push(item);
      console.log(arrayOG);
    } else if (re2.test(item) == true && item.length > 3) {
      arrayAT.push(item);
      console.log(arrayAT);
    } else if (re3.test(item) == true) {
      arrayNumberFirst.push(item);
      console.log(arrayNumberFirst);
    } else if (re4.test(item) == true) {
      arrayNumberLast.push(item);
      console.log(arrayNumberLast);
    }
  }
}
loop();

Answer 1

您在函数定义中将 item 声明为函数参数
函数循环(项目){
但稍后当调用函数 loop() 时，您实际上并没有传递任何内容。
然后，对于循环的每次迭代，项目都是未定义的。
而不是

function loop(item) {
  for (var i = 0; i < mainList.length; i++) {
    ...
  }
}

你应该尝试

function loop() {
  for (var i = 0; i < mainList.length; i++) {
    const item = mainList[i];
    ...
  }
}