Javascript Uncaught TypeError：无法读取未定义的属性“ length”（使用数组）

Question

我有一个数组设置，它将两个参数传递给函数。 但是，当我使用console.log时，出现异常。 奇怪的是，如果我要从参数中删除参数，它将运行，这是他们的任何原因吗，我该如何解决？

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

您必须在调用函数时将参数传递给函数。

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

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，首先是调用函数的代码，然后是函数。 如果您使用更多功能，则会失去对工作的跟踪，或者更糟的是会开始出错，

 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; } 

Answer 3

说明：在声明带有参数的函数时，这些参数将成为局部参数。 这意味着，即使您有一些名称为musicians and instruments变量，函数中具有相同名称的参数仍将被视为局部变量。

要解决您的问题，您有两种方法：

1. 删除函数声明语句中的参数（原来您想访问那些在函数外部声明的变量，因此您不需要为函数使用参数）：

    var musicians = ["Paul", "John", "Yuri"], instruments = ["Drums", "Guitar", "Chelo"]; /* Precondition: defined musicians and instruments arrays outside of a function */ function theBeatlesPlay(/* No params */) { var empty = []; for (var i = 0; i < musicians.length; i++) { var str = musicians[i] + " plays " + instruments[i]; empty = str; console.log(empty); } } 

2. 调用传递给它的函数，该函数先前声明了两个数组：

    /* musicians and instruments variables are LOCAL for the function in this case */ 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); 

我也强烈建议您不要命名为empty变量，因为最初它是空的。 否则，它应该是一个常数。

顺便说一句，分析抛出什么类型的异常以及它提供什么消息是很有用的。