function solution(s) {
var c = s[0];

if (c == c.toUpperCase() && !(c >= '0' && c <= '9') &&(c >='A' && c <= 'Z')) {
    return 'upper';
} else if (c == c.toLowerCase() && !(c >= '0' && c <= '9') &&(c >='a' && c <= 'z')){
    return 'lower';
} else if (c >= '0' && c <= '9'){
   return 'digit'
} else {
  return 'other' 
}
}

var str1= (solution('A')) // upper
var str2 = solution('b') // lower
var str3 = solution('1') // digit
var str4 = solution('_') // other
console.log(`${str1} ${str2} ${str3} ${str4}`)

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;
}

const isUpperCase = (string) => /^[A-Z]*$/.test(string)

然后:

isUpperCase('A') // true
isUpperCase('a') // false

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

我需要测试任何字符的字符串(包括空白，标记，数字，unicode字符…)因为空白、数字、标记……大写字母和小写字母都是一样的，我想找到真正的大写字母，我这样做:

let countUpperCase = 0;
let i = 0;
while (i <= string.length) {
  const character = string.charAt(i);
  if (character === character.toUpperCase() && character !== character.toLowerCase()) {
    countUpperCase++;
  }
  i++;
}

if (character == character.toLowerCase())
{
  // The character is lowercase
}
else
{
  // The character is uppercase
}