Cannot read properties of undefined (reading 'toLowerCase')

This error message typically indicates that you are trying to call the `toLowerCase()` method on a variable that is undefined.

For example, if you have a variable called `myString` and you try to call `myString.toLowerCase()`, but `myString` is undefined, you will get this error message.

To fix this error, you need to make sure that the variable you are calling `toLowerCase()` on is defined and has a value. You can use an if statement or a try-catch block to handle cases where the variable may be undefined.

相关问题

Cannot read properties of undefined (reading 'toLowerCase') TypeError: Cannot read properties of undefined (reading 'toLowerCase')

这个错误通常是由于尝试在未定义的变量上调用方法或属性而引起的。在这种情况下，代码尝试在未定义的变量上调用 toLowerCase() 方法，因此会抛出 TypeError: Cannot read properties of undefined (reading 'toLowerCase') 错误。要解决这个问题，你需要确保在调用 toLowerCase() 方法之前，变量已经被正确地定义和初始化了。

如果你能提供更多的代码或上下文信息，我可以更具体地帮助你解决这个问题。

VM18:71 Uncaught TypeError: Cannot read properties of undefined (reading toLowerCase )

VM18:71这个错误信息通常出现在JavaScript环境中，"TypeError: Cannot read properties of undefined (reading 'toLowerCase')"表明开发者试图访问一个未定义对象的`toLowerCase`属性。这里的`toLowerCase`是一个字符串方法，用于将字符串转换为小写。当你尝试对null、undefined或者其他非字符串值调用这个方法时，就会抛出这个错误。

举个例子：

let str; // 这里str是undefined
console.log(str.toLowerCase()); // 这会抛出错误，因为str是未定义的

修复此错误的方法是在访问`toLowerCase`之前检查变量是否已定义并且非空：

let str = '';
if (typeof str !== 'undefined' && str !== null) {
    console.log(str.toLowerCase());
}