[英]Determining the case (upper/lower) of the first letter in a string
在Web应用程序中,如何使用JavaScript确定给定字符串中的第一个字母是大写还是小写?
You can use toUpperCase
: 你可以使用toUpperCase
:
if(yourString.charAt(0) === yourString.charAt(0).toUpperCase()) {
//Uppercase!
}
If you're going to be using this on a regular basis, I would suggest putting it in a function on the String prototype, something like this: 如果您将定期使用它,我建议将它放在String原型的函数中,如下所示:
String.prototype.isFirstCapital = function() {
return this.charAt(0) === this.charAt(0).toUpperCase();
}
if(yourString.isFirstCapital()) {
//Uppercase!
}
Update (based on comments) 更新 (根据评论)
I don't know what you actually want to do in the case that the string does not being with a letter, but a simple solution would be to add a quick check to see if it does or not, and return false if not: 在字符串没有字母的情况下,我不知道你真正想做什么,但一个简单的解决方案是添加一个快速检查以确定它是否有,如果没有则返回false:
String.prototype.isFirstCapital = function() {
return /^[a-z]/i.test(this) && this.charAt(0) === this.charAt(0).toUpperCase();
}
This will work only with English alphabet. 这只适用于英文字母。
var ch = myStr.chatAt(0);
if (ch >= 'a' && ch <= 'z') {
// small
} else if (ch >= 'A' && ch <= 'Z') {
// capital
} else {
// not english alphabet char
}
This will be called recursively until a first letter in a string is approached, otherwise returns 'no letters'
. 这将被递归调用,直到接近字符串中的第一个字母,否则返回'no letters'
。
function getFirstCase(string) {
if (string === '') return 'no letters';
var firstChar = string.charAt(0);
/*
* If both lowercase and uppercase
* are equal, it is not a letter
*/
if (firstChar.toLowerCase() === firstChar.toUpperCase()) {
return getFirstCase(string.substr(1));
} else {
return firstChar.toLowerCase() === firstChar ? 'lowercase' : 'uppercase';
}
}
Testing: 测试:
console.log(getFirstCase('alphabet'),
getFirstCase('Sunshine'),
getFirstCase('123123'),
getFirstCase('@Hi'),
getFirstCase('\nHAHA'));
var mystring = "Test string";
var first= "";
if (mystring )
{
first= mystring[1];
}
if (first)
{
$('p').each(function()
{
if ($(this).text().charAt(0).toUpperCase() === $(this).text().charAt(0))
{
alert("Uppercase");
}
});
}
I'm surprised no one's offered a regex solution to this - it seems like the easiest by far: 我很惊讶没有人提供这方面的正则表达式解决方案 - 它似乎是最简单的:
function getFirstCase(s) {
return (/^[\d\W]*[A-Z]/).test(s) ? 'upper' :
(/^[\d\W]*[a-z]/).test(s) ? 'lower' :
'none';
}
Blatantly stealing @Lapple's test cases: 公然窃取@ Lapple的测试用例:
console.log(getFirstCase('alphabet'),
getFirstCase('Sunshine'),
getFirstCase('123123'),
getFirstCase('@Hi'),
getFirstCase('\nHAHA'));
// lower upper none upper upper
See http://jsfiddle.net/nrabinowitz/a5cQa/ 见http://jsfiddle.net/nrabinowitz/a5cQa/
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