有人可以解释代码中发生了什么？

Question

我想猜猜用户输入什么类型的字母。

var userLetter = prompt("Enter a letter and I will tell you what type of letter is","Enter here, wish me luck!"); 

function selectUserLetter(letter) { 
    var returnType = "NA"; 

    if (userLetter.charCodeAt(0) >= "A".charCodeAt(0) && userLetter.charCodeAt(0) <= "Z".charcodeAt(0)) { 
     returnType = "U"; 
    } 
    else if (userLetter.charCodeAt(0) >= "a".charCodeAt(0) && userLetter.charCodeAt(0) <= "z".charcodeAt(0)) { 
     returnType = "L"; 
    } 
    else if (userLetter.charCodeAt(0) >= "0".charCodeAt(0) && userLetter.charCodeAt(0) <= "9".charcodeAt(0)) { 
     returnType = "N"; 
    } 

    return returnType; 
} 

switch (selectUserLetter(userLetter)) { 
    case "U": 
     document.write("Your letter is Uppercase"); 
     break; 

    case "L": 
     document.write("Your letter is Lowercase"); 
     break; 

    case "N": 
     document.write("Your letter is a number"); 
     break; 

    default: 
     document.write("You typed anything else"); 
} 

Answer 1

在代码中，片段"Z".charcodeAt，"z".charcodeAt(0)和"9".charcodeAt(0)由charcodeAt函数调用。问题在于JavaScript是大小写繁杂的语言。所以，charcodeAt不存在，而不是charCodeAt。