我相信这是最简单的解决办法。你可以在输入字段中使用onchange处理程序。进行验证

const isValid = e.target.value === e.target.value.toLowerCase()

if (isValid) {
  //Do something
} else {
  //Do something
}

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()); 
}

你可以使用正则表达式测试和toUpperCase方法:

String.prototype.charAtIsUpper = function (atpos){
      var chr = this.charAt(atpos);
      return /[A-Z]|[\u0080-\u024F]/.test(chr) && chr === chr.toUpperCase();
};
// usage (note: character position is zero based)
'hi There'.charAtIsUpper(3);      //=> true
'BLUE CURAÇAO'.charAtIsUpper(9);  //=> true
'Hello, World!'.charAtIsUpper(5); //=> false

另请参阅

您可以通过使用match方法和regex测试数组是否具有大写或小写字符串，下面只是开始测试的基本基础

  var array = ['a', 'b', 'c', 'A', 'B', 'C', '(', ')', '+', '-', '~', '*'];
  var character = array.join('')
      console.log(character)

  var test = function(search){
      upperCase = search.match(/[A-Z]/g)
      console.log(upperCase)

      lowerCase = search.match(/[a-z]/g)
      console.log(lowerCase)
   }

   test(character)

Stephen Nelsons的函数转换成带有大量测试示例的原型。

为了完整起见，我还在函数中添加了整个字符串。

有关其他注释，请参阅代码。

/* Please note, there's no requirement to trim any leading or trailing white spaces. This will remove any digits in the whole string example returning the correct result. */ String.prototype.isUpperCase = function(arg) { var re = new RegExp('\\s*\\d+\\s*', 'g'); if (arg.wholeString) {return this.replace(re, '') == this.replace(re, '').toUpperCase()} else return !!this && this != this.toLocaleLowerCase(); } console.log('\r\nString.prototype.isUpperCase, whole string examples'); console.log(' DDD is ' + ' DDD'.isUpperCase( { wholeString:true } )); console.log('9 is ' + '9'.isUpperCase( { wholeString:true } )); console.log('Aa is ' + 'Aa'.isUpperCase( { wholeString:true } )); console.log('DDD 9 is ' + 'DDD 9'.isUpperCase( { wholeString:true } )); console.log('DDD is ' + 'DDD'.isUpperCase( { wholeString:true } )); console.log('Dll is ' + 'Dll'.isUpperCase( { wholeString:true } )); console.log('ll is ' + 'll'.isUpperCase( { wholeString:true } )); console.log('\r\nString.prototype.isUpperCase, non-whole string examples, will only string on a .charAt(n) basis. Defaults to the first character'); console.log(' DDD is ' + ' DDD'.isUpperCase( { wholeString:false } )); console.log('9 is ' + '9'.isUpperCase( { wholeString:false } )); console.log('Aa is ' + 'Aa'.isUpperCase( { wholeString:false } )); console.log('DDD 9 is ' + 'DDD 9'.isUpperCase( { wholeString:false } )); console.log('DDD is ' + 'DDD'.isUpperCase( { wholeString:false } )); console.log('Dll is ' + 'Dll'.isUpperCase( { wholeString:false } )); console.log('ll is ' + 'll'.isUpperCase( { wholeString:false } )); console.log('\r\nString.prototype.isUpperCase, single character examples'); console.log('BLUE CURAÇAO'.charAt(9) + ' is ' + 'BLUE CURAÇAO'.charAt(9).isUpperCase( { wholeString:false } )); console.log('9 is ' + '9'.isUpperCase( { wholeString:false } )); console.log('_ is ' + '_'.isUpperCase( { wholeString:false } )); console.log('A is ' + 'A'.isUpperCase( { wholeString:false } )); console.log('d is ' + 'd'.isUpperCase( { wholeString:false } )); console.log('E is ' + 'E'.isUpperCase( { wholeString:false } )); console.log('À is ' + 'À'.isUpperCase( { wholeString:false } )); console.log('É is ' + 'É'.isUpperCase( { wholeString:false } )); console.log('Ñ is ' + 'Ñ'.isUpperCase( { wholeString:false } )); console.log('ñ is ' + 'ñ'.isUpperCase( { wholeString:false } )); console.log('Þ is ' + 'Þ'.isUpperCase( { wholeString:false } )); console.log('Ͻ is ' + 'Ͻ'.isUpperCase( { wholeString:false } )); console.log('Ͽ is ' + 'Ͽ'.isUpperCase( { wholeString:false } )); console.log('Ά is ' + 'Ά'.isUpperCase( { wholeString:false } )); console.log('Έ is ' + 'Έ'.isUpperCase( { wholeString:false } )); console.log('ϴ is ' + 'ϴ'.isUpperCase( { wholeString:false } )); console.log('Ϋ is ' + 'Ϋ'.isUpperCase( { wholeString:false } )); console.log('Ϣ is ' + 'Ϣ'.isUpperCase( { wholeString:false } )); console.log('Ϥ is ' + 'Ϥ'.isUpperCase( { wholeString:false } )); console.log('Ϧ is ' + 'Ϧ'.isUpperCase( { wholeString:false } )); console.log('Ϩ is ' + 'Ϩ'.isUpperCase( { wholeString:false } )); console.log('Ϫ is ' + 'Ϫ'.isUpperCase( { wholeString:false } )); console.log('Ϭ is ' + 'Ϭ'.isUpperCase( { wholeString:false } )); console.log('Ϯ is ' + 'Ϯ'.isUpperCase( { wholeString:false } )); console.log('Ϲ is ' + 'Ϲ'.isUpperCase( { wholeString:false } )); console.log('Ϸ is ' + 'Ϸ'.isUpperCase( { wholeString:false } )); console.log('Ϻ is ' + 'Ϻ'.isUpperCase( { wholeString:false } ));

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

然后:

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