还可以使用正则表达式显式地检测大写罗马字母字符。

isUpperCase = function(char) {
  return !!/[A-Z]/.exec(char[0]);
};

EDIT:上面的函数对ASCII/基本拉丁Unicode是正确的，这可能是你所关心的。以下版本还支持拉丁-1补充和希腊和科普特Unicode块…以防你因为什么原因需要它。

isUpperCase = function(char) {
  return !!/[A-ZÀ-ÖØ-ÞΆΈ-ΏΑ-ΫϢϤϦϨϪϬϮϴϷϹϺϽ-Ͽ]/.exec(char[0]);
};

如果您需要进一步的支持(Ѭ是大写的吗?)，这个策略就会失效，因为有些块会混合大小写字符。

假设一个字符串只有在至少有一个小写字母的情况下才被认为不全是大写，这可以正常工作。我知道它不像其他人试图做的那样简洁，但它有效吗=)

function isUpperCase(str) {
    for (var i = 0, len = str.length; i < len; i++) {
        var letter = str.charAt(i);
        var keyCode = letter.charCodeAt(i);
        if (keyCode > 96 && keyCode < 123) {
            return false;
        }
    }

    return true;
}

更确切地说，是关于被问到的问题。传入一个字符串和一个要检查的位置。和Josh的很接近，只是这个比较的是更大的字符串。会添加作为一个评论，但我还没有这个能力。

function isUpperCase(myString, pos) { 
    return (myString.charAt(pos) == myString.charAt(pos).toUpperCase()); 
}   

function isLowerCase(myString, pos) {
    return (myString.charAt(pos) == myString.charAt(pos).toLowerCase()); 
}

这是直接的，可读的解决方案使用一个简单的正则表达式。

// Get specific char in string
const char = string.charAt(index);

const isLowerCaseLetter = (/[a-z]/.test(char));
const isUpperCaseLetter = (/[A-Z]/.test(char));

你也可以使用这个，它将检查字符串的小写字母和大写字母

var s = "a"
if(/[a-z]/.test(s)){
  alert ('lower case true');
}

if(/[A-Z]/.test(s)) {
 alert ('upper case true'); 
}

function checkCharType (charToCheck) {
    // body... 
    var returnValue = "O";
    var charCode = charToCheck.charCodeAt(0);

    if(charCode >= "A".charCodeAt(0) && charCode <= "Z".charCodeAt(0)){

        returnValue = "U";

    }else if (charCode >= "a".charCodeAt(0) &&
                charCode <= "z".charCodeAt(0) ){
        returnValue = "L";
    }else if (charCode >= "0".charCodeAt(0) &&
            charCode <= "9".charCodeAt(0)  ) {
        returnValue = "N";
    }
    return returnValue;
}

var myString = prompt("Enter Some text: ", "Hello world !");

switch (checkCharType(myString)) {
    case "U":
        // statements_1
        document.write("First character was upper case");
        break;

    case "L":
        document.write("First character was a lower case");
        break;
    case "N":
        document.write("First character was a number");
        break
    default:
        // statements_def
        document.write("First character was not a character or a number");
        break;
}

Define a Function checkCharType().By declaring the variable returnValue and initialising it to the Character "O" to indicate it's Some other value. U for uppercase; L for Lowercase ; N for number Use the charCodeAt() method to get the character code of the first character. Using if Statement , which check within what range of values the character code falls. If it falls between the character codes for A and Z, Its Uppercase, character code between a and z ,Its Lowercase. and so on. "A".charCode(0) var myChar = new String("A"); myChar.charCodeAt(0); "A" : number code "65“ Check the String