检查第一个字母是否是大写字母

Is it possible in Javascript to find out if the first letter of a word is a capital letter?

是否有可能在Javascript中找出单词的第一个字母是否是大写字母？

7 个解决方案

#1

var word = "Someword";
console.log( word[0] === word[0].toUpperCase() );

or

要么

var word = "Someword";
console.log( /[A-Z]/.test( word[0]) );

or

要么

var word = "Someword";
console.log( /^[A-Z]/.test( word) );

See toUpperCase() and test()

请参阅toUpperCase（）和test（）

#2

The other answers on this page are fine for strings that are known to only contain non-accented A-Z letters. If you can't guarantee this (e.g. user input), they may give unexpected results: false positives for uncapitalisable initials like "1940s" or "中文", or false negatives for accented or non-Roman capital initials like "Łukasz" or "Александра".

此页面上的其他答案适用于已知仅包含非重音A-Z字母的字符串。如果你不能保证这一点（例如用户输入），它们可能会产生意想不到的结果：对于像“1940年代”或“中文”这样的不可开头的首字母的误报，或者对于“Łukasz”或“Łukasz”或“罗马”等首字母缩写的假阴性Александра”。

This variant returns true if the initial is any capital letter, and only if it's a capital letter:

如果首字母是任何大写字母，并且仅当它是大写字母时，此变量返回true：

function initialIsCapital( word ){
  return word[0] !== word[0].toLowerCase();
}

Use .charAt(0) instead of [0] if you need IE8 support. Which is faster varies between browsers.

如果需要IE8支持，请使用.charAt（0）而不是[0]。哪个浏览器的速度更快。

This avoids two potential pitfalls with the other answers:

这避免了其他答案的两个潜在缺陷：

• Regexes using [A-Z] will fail to match accented and other similar non-A-Z capitalised letters such as in Åland (Scandinavian islands) and Łukasz (common Polish name), including capital letters in non-latin scripts such as Cyrillic or Greek (e.g. Александра).

  使用[AZ]的正则表达式将无法匹配重音和其他类似的非AZ大写字母，例如Åland（斯堪的纳维亚群岛）和Łukasz（常见的波兰语名称），包括西里尔语或希腊语等非拉丁文字母（例如Александра） ）。

• The approach using word[0] === word[0].toUpperCase(), will return true on words that start with non-letters, such as 1940s, 17th, 123reg (company name), abbreviations like 2mrw, or some words in some African languages, such as !xūún or ǂǐ-sì. It'll also treat any input from an alphabet that doesn't have capital letters as being capital letters (e.g. 中文).

  使用word [0] === word [0] .toUpperCase（）的方法将在以非字母开头的单词上返回true，例如1940s，17th，123reg（公司名称），缩写如2mrw或某些单词在某些非洲语言中，例如！xūún或ǂǐ-sì。它还会将字母表中没有大写字母的任何输入视为大写字母（例如中文）。

Since this arbitrary-input-safe approach is just as simple and no less readable than the alternatives, it's probably better to use this even if you don't anticipate such exceptions.

由于这种任意输入安全方法与替代方法一样简单且可读性差，因此即使您不预期此类异常，也可能更好地使用它。

Here's a quick test:

这是一个快速测试：

function a(word){
  return word[0] !== word[0].toLowerCase();
}
function b(word){
  return word[0] === word[0].toUpperCase();
}
function c(word){
  return /^[A-Z]/.test( word );
}
function test(word, answer){
  console.log( 'Should be '+answer+':',  a(word), b(word), c(word), '-------', word );
}

test( 'Łukasz', true ); // regex test fails, returns false
test( 'Александра', true ); // regex test fails, returns false
test( '1940s', false ); // .toUpperCase() test fails, returns true
test( '中文', false ); // .toUpperCase() test fails, returns true

test( 'ß', false ); // All pass on German "sharp S" that has no uppercase
test( 'Z̢̜̘͇̹̭a͎͚͔͕̩̬̭͈͞l̩̱̼̤̣g̲̪̱̼̘̜͟ợ̮̱͎̗̕ͅͅ', true ); // All pass. Phew, Zalgo not awakened 

#3

Yes.

是。

var str = "Hello";
if(str[0].toUpperCase() == str[0])
{
   window.alert('First character is upper case.');  
}

#4

You can do it in several ways:

您可以通过以下几种方式实现：

var myWord = "Hello";

// with string functions
if (myWord.charAt(0) === myWord.charAt(0).toUpperCase()) { /* is upper */ }

// or for newer browsers that support array-style access to string characters
if (myWord[0] === myWord[0].toUpperCase()) { /* is upper */ }

// with regex - may not be appropriate for non-English uppercase
if (/^[A-Z]/.test(myWord) { /* is upper */ }

Note that the array-style access to characters like myWord[0] is an ECMAScript 5 feature and not supported in older browsers, so (for now) I'd probably recommend the .charAt() method.

请注意，对myWord [0]等字符的数组样式访问是ECMAScript 5的一项功能，在旧版浏览器中不受支持，所以（现在）我可能会推荐使用.charAt（）方法。

If you need to do this test a lot you could make a little function:

如果你需要做很多测试，你可以做一点功能：

function firstLetterIsUpper(str) {
   var f = str.charAt(0);   // or str[0] if not supporting older browsers
   return f.toUpperCase() === f;
}

if (firstLetterIsUpper(myWord)) { /* do something */ }

#5

For English letters only:

仅限英文字母：

'A' => 65
'Z' => 90

Meaning, every number between [65, 90] is a capital letter:

意思是，[65,90]之间的每个数字都是大写字母：

function startsWithCapitalLetter(word) {
  return word.charCodeAt(0) >= 65 && word.charCodeAt(0) <= 90;
}

#6

var string1 = "this is a string";
var string2 = "This is a string";

if(string1[0] == string1[0].toUpperCase())
    alert('is upper case');
else
    alert('is not upper case');


if(string2[0] == string2[0].toUpperCase())
    alert('is upper case');
else
    alert('is not upper case');

#7

let word = 'Someword';
console.log(word.match(new RegExp(/^[A-Z]/)) !== null);