Question

Javascript 未捕获的类型错误：无法读取未定义的属性“length”（使用数组）

2017-04-15

2569

javascript arrays

我设置了一个数组，它将两个参数传递给函数。但是，当我使用 console.log 时，我得到了一个异常。这很奇怪，因为如果我从参数中删除参数，它就会运行，这有什么原因吗？我该如何修复它？

var musicians = ["Paul", "John", "Yuri"];

var instruments = ["Drums", "Guitar", "Chelo"];

function theBeatlesPlay(musicians, instruments) {

    var empty = [];

    for (var i = 0; i < **musicians.length**; i++) {

      var str = musicians[i] + " plays " + instruments[i];
      empty = str;
      **console.log(empty)**;
    }
    }

    theBeatlesPlay();

Answer 1

调用函数时，必须将参数传递给该函数。

theBeatlesPlay(musicians, Instruments);

var musicians = ["Paul", "John", "Yuri"],
    instruments = ["Drums", "Guitar", "Chelo"];

function theBeatlesPlay(musicians, instruments) {
  var empty = [];
  for (var i = 0; i < musicians.length; i++) {
    var str = musicians[i] + " plays " + instruments[i];
    empty = str;
    console.log(empty);
  }
}

theBeatlesPlay(musicians, instruments);

Answer 2

解释：当您声明带有参数的函数时，这些参数将成为本地参数。这意味着，即使您有一些名为 musicians 和 instruments 的变量，函数中具有相同名称的参数仍将被视为本地

要解决您的问题，您有两种方法：

删除函数声明语句中的参数（事实证明您想要访问在函数外部声明的那些变量，因此您的函数不需要参数）：

var musicals = ["Paul", "John", "Yuri"],
instruments = ["Drums", "Guitar", "Chelo"];

/* 前提条件：在函数外部定义 musicals 和 musicals 数组 */
function theBeatlesPlay(/* 无参数 */) {

var empty = [];

for (var i = 0; i < musicals.length; i++) {

var str = musicals[i] + " plays " + musicals[i];
empty = str;
console.log(empty);
}
}

调用函数，将之前声明的两个数组传递给它：

/*
在这种情况下，musicians 和 musicals 变量是函数的本地变量
*/
function theBeatlesPlay(musicians, musicals) {

var empty = [];

for (var i = 0; i < musicals.length; i++) {

var str = musicals[i] + " plays " + musicals[i];
empty = str;
console.log(empty);
}
}

theBeatlesPlay(musicians, musicals);

我还强烈建议您不要将变量命名为 empty ，因为它最初是空的。否则它应该是一个常量。

顺便说一句，分析抛出的异常类型及其提供的消息很有用。

Answer 3

您的问题是您没有将参数传递给函数。使用函数的正确方法是首先调用函数的代码，然后是函数。如果您使用更多函数，您将忘记自己在做什么，或者更糟的是会开始出现错误，

var musicians = ["Paul", "John", "Yuri"];

var instruments = ["Drums", "Guitar", "Chelo"];

var errlog = theBeatlesPlay(musicians, instruments);

console.log(errlog);

function theBeatlesPlay(musicians_val, instruments_val) {

var empty = [];

for (var i = 0; i < musicians_val.length; i++) {

var str = musicians_val[i] + " plays " + instruments_val[i];
      empty = str;
     
    }
    return empty;
 }