What's wrong with JavaScript not being able to retrieve uppercase letters?

JavaScript generally retrieves all characters in a string, including uppercase and lowercase letters. However, if there is a situation where uppercase letters cannot be retrieved, then we need to consider the following situations:

1. First, we need to confirm whether the string actually contains uppercase letters. If the string contains only lowercase letters, uppercase letters cannot be retrieved when we use case-insensitive retrieval methods.
2. Check whether the retrieval method we use is case-sensitive. There are many retrieval methods in JavaScript, some are case-sensitive and some are not. For example, the indexOf() method is case-sensitive by default, while the toLowerCase() method converts the string to lowercase.
3. It may be a code problem. If there is no problem with the retrieval method and syntax we used, then there may be other errors in the code. We can check to see if other operations interspersed in the code have modified the string or not converted cases correctly.

There are many ways to solve these problems. Here are some common solutions:

1. Before using the retrieval method, you can first convert the string to lowercase or uppercase letter. This can be achieved by using the toLowerCase() or toUpperCase() methods. For example: var str = "HELLO WORLD!"; str = str.toLowerCase(); Then we can successfully retrieve uppercase letters in the string.
2. If you need to perform case-insensitive retrieval, you can use regular expressions, using the flag "i" to specify case-insensitive retrieval. For example: var str = "HELLO WORLD!"; var regex = /hello/i; if(regex.test(str)){ console.log("Successful match!"); }
3. Check the code Other errors that may exist to determine the cause of the problem and resolve it promptly.

In short, the problem of inability to retrieve uppercase letters can occur in many places, and we should thoroughly check and debug the code and adopt reasonable solutions. As long as we focus on solving the problem, we will be able to find the best solution.

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