使用 else if 语句检查大写、小写或数字字符 [关闭]

Question

我一直在尝试解决这个问题以检查字符是大写、小写还是数字，我已经能够为大写和小写做到这一点，但我不能为数字做到这一点.

let letterOrNumber = prompt("Enter an uppercase letter, a lowercase letter or a number");

let upperCaseLetter = letterOrNumber.toUpperCase();
let lowerCaseLetter = letterOrNumber.toLowerCase();
let userNumber = parseInt(letterOrNumber)

if (letterOrNumber === upperCaseLetter) {
    console.log(letterOrNumber + " is an uppercase letter.");
}

else if (letterOrNumber === lowerCaseLetter) {
    console.log(letterOrNumber + " is a lowercase letter.");
}

else if (letterOrNumber === userNumber) {
    console.log(letterOrNumber + " is a number.");
}

else {
    console.log(letterOrNumber + " is not a letter or number");
}

Answer 1

对于单个字符串字符，您可以使用 !isNaN（not 不是数字）。
另外，请确保在匹配 Alpha 字符之前先去掉 Numerics

const letterOrNumber = prompt("Enter an uppercase letter, a lowercase letter or a number");

const upperCaseLetter = letterOrNumber.toUpperCase();
const lowerCaseLetter = letterOrNumber.toLowerCase();
const isNum = !isNaN(letterOrNumber);

if (isNum) {
  console.log(letterOrNumber + " is a number.");
} else if (letterOrNumber === upperCaseLetter) {
  console.log(letterOrNumber + " is an uppercase letter.");
} else if (letterOrNumber === lowerCaseLetter) {
  console.log(letterOrNumber + " is a lowercase letter.");
} else {
  console.log(letterOrNumber + " is not a letter or number");
}

Answer 2

使用isNaN判断是否为数字。

let letterOrNumber = prompt("Enter an uppercase letter, a lowercase letter or a number");

let upperCaseLetter = letterOrNumber.toUpperCase();
let lowerCaseLetter = letterOrNumber.toLowerCase();


if (!isNaN(letterOrNumber)) {
  console.log(letterOrNumber + " is a number.");
} else if (letterOrNumber === upperCaseLetter) {
  console.log(letterOrNumber + " is an uppercase letter.");
} else if (letterOrNumber === lowerCaseLetter) {
  console.log(letterOrNumber + " is a lowercase letter.");
} else {
  console.log(letterOrNumber + " is not a letter or number");
}

Answer 3

除了其他答案之外，我还想指出，您的代码目前不适用于数字大小写的原因是因为您将字符串 letterOrNumber 与 userNumber 进行比较，这是一个数字。类型不匹配。因此，条件为 false 并转到 else 分支。

Answer 4

另一种方法是对match 大写字符、小写字符或数字使用正则表达式。此方法将捕获_ 之类的字符或Š 之类的带有变音符号的字符，并为它们适当地记录输出。

function check(str = '') {

  const regex = /([A-ZÀ-ž])|([a-zà-ž])|([0-9])/;
  const match = str.match(regex);

  // `match` returns an array, so if it exists (has length)
  if (match) {

    // `slice` off the first element (which is the complete match)
    // and then find the index of the element which isn't undefined
    const index = match.slice(1).findIndex(el => el);

    // You can then log the result based on the index
    switch(index) {
      case 0: return 'Uppercase';
      case 1: return 'Lowercase';
      case 2: return 'Number';
    }
  }

  // Returns "none` if there is no match
  return 'None';

}

console.log(check('_'));
console.log(check('1'));
console.log(check('ž'));
console.log(check('A'));
console.log(check('z'));
console.log(check('+'));
console.log(check('/'));
console.log(check('B'));
console.log(check('Š'));
console.log(check(undefined));