我正在使用以下方法提取Javascript字符串中的字符:
var first = str.charAt(0);
我想检查一下是否是字母。奇怪的是,Javascript中似乎不存在这种功能。至少我找不到它。
我该如何测试?
我正在使用以下方法提取Javascript字符串中的字符:
var first = str.charAt(0);
我想检查一下是否是字母。奇怪的是,Javascript中似乎不存在这种功能。至少我找不到它。
我该如何测试?
Answers:
我相信这个插件具有您想要的功能:http : //xregexp.com/plugins/(github链接:https : //github.com/slevithan/xregexp)
有了它,您可以简单地将所有unicode字母与匹配\p{L}
。
阅读此源文件的标题以查看其支持的类别:http : //xregexp.com/plugins/xregexp-unicode-categories.js
我不相信有内置功能。但是用正则表达式编写起来很容易
function isLetter(str) {
return str.length === 1 && str.match(/[a-z]/i);
}
var char=str.toLowerCase(); return (char.length==1 && char>='a' && char<='z')
str
是来自z的值,它将返回该值。否则,它返回null。如果您需要它返回true / false,请使用它。 isLetter: function (str) { if (str.length !== 1 && str.match(/[a-z]/i)) { return true; } return false; },
对于诸如之类的较简单检查未考虑的特殊字符/[a-zA-Z]/.test(c)
,利用ECMAScript大小写转换(toUpperCase
)可能是有益的。它将考虑某些外来字母的非ASCII Unicode字符类。
function isLetter(c) {
return c.toLowerCase() != c.toUpperCase();
}
注意:此解决方案仅适用于大多数拉丁,希腊,亚美尼亚和西里尔文字。它不适用于中文,日文,阿拉伯文,希伯来文和其他大多数文字。
/[a-z]/i
模式,此技巧将接受完整范围的拉丁字符。与其他包含完整拉丁Unicode上下映射的解决方案相比,您节省了99.2%的代码大小。将此解决方案称为“错误”是一种误导,因为它取决于您的问题。如果您的范围是拉丁字符集,则这是一种精巧而优雅的解决方法。
if( char.toUpperCase() != char.toLowerCase() )
仅在字母的情况下才返回true
正如下面的注释中指出的那样,如果您的字符是非英语,高ASCII或双字节范围,则需要添加代码点检查。
if( char.toUpperCase() != char.toLowerCase() || char.codePointAt(0) > 127 )
1a
例如,这是为了防止。
如何使用ASCII码?
let n = str.charCodeAt(0);
let strStartsWithALetter = (n >= 65 && n < 91) || (n >= 97 && n < 123);
该解决方案与工作的特殊字符太多,例如é
,è
,ê
,ü
,ö
,à
2个步骤:
我的解决方案的现场演示:
注意:我发布了使用全局函数的解决方案,因为它可能是最容易理解的。但是,如果您想要更好的代码(更干净,更易于维护和扩展),请查看“ javascript模块模式”,请参阅令人印象深刻的webs.com/my-current-javascript-design-pattern以及此YouTube视频(由Paul Irish演示)。
var defaultDiacriticsRemovalap = [
{'base':'A', 'letters':'\u0041\u24B6\uFF21\u00C0\u00C1\u00C2\u1EA6\u1EA4\u1EAA\u1EA8\u00C3\u0100\u0102\u1EB0\u1EAE\u1EB4\u1EB2\u0226\u01E0\u00C4\u01DE\u1EA2\u00C5\u01FA\u01CD\u0200\u0202\u1EA0\u1EAC\u1EB6\u1E00\u0104\u023A\u2C6F'},
{'base':'AA','letters':'\uA732'},
{'base':'AE','letters':'\u00C6\u01FC\u01E2'},
{'base':'AO','letters':'\uA734'},
{'base':'AU','letters':'\uA736'},
{'base':'AV','letters':'\uA738\uA73A'},
{'base':'AY','letters':'\uA73C'},
{'base':'B', 'letters':'\u0042\u24B7\uFF22\u1E02\u1E04\u1E06\u0243\u0182\u0181'},
{'base':'C', 'letters':'\u0043\u24B8\uFF23\u0106\u0108\u010A\u010C\u00C7\u1E08\u0187\u023B\uA73E'},
{'base':'D', 'letters':'\u0044\u24B9\uFF24\u1E0A\u010E\u1E0C\u1E10\u1E12\u1E0E\u0110\u018B\u018A\u0189\uA779'},
{'base':'DZ','letters':'\u01F1\u01C4'},
{'base':'Dz','letters':'\u01F2\u01C5'},
{'base':'E', 'letters':'\u0045\u24BA\uFF25\u00C8\u00C9\u00CA\u1EC0\u1EBE\u1EC4\u1EC2\u1EBC\u0112\u1E14\u1E16\u0114\u0116\u00CB\u1EBA\u011A\u0204\u0206\u1EB8\u1EC6\u0228\u1E1C\u0118\u1E18\u1E1A\u0190\u018E'},
{'base':'F', 'letters':'\u0046\u24BB\uFF26\u1E1E\u0191\uA77B'},
{'base':'G', 'letters':'\u0047\u24BC\uFF27\u01F4\u011C\u1E20\u011E\u0120\u01E6\u0122\u01E4\u0193\uA7A0\uA77D\uA77E'},
{'base':'H', 'letters':'\u0048\u24BD\uFF28\u0124\u1E22\u1E26\u021E\u1E24\u1E28\u1E2A\u0126\u2C67\u2C75\uA78D'},
{'base':'I', 'letters':'\u0049\u24BE\uFF29\u00CC\u00CD\u00CE\u0128\u012A\u012C\u0130\u00CF\u1E2E\u1EC8\u01CF\u0208\u020A\u1ECA\u012E\u1E2C\u0197'},
{'base':'J', 'letters':'\u004A\u24BF\uFF2A\u0134\u0248'},
{'base':'K', 'letters':'\u004B\u24C0\uFF2B\u1E30\u01E8\u1E32\u0136\u1E34\u0198\u2C69\uA740\uA742\uA744\uA7A2'},
{'base':'L', 'letters':'\u004C\u24C1\uFF2C\u013F\u0139\u013D\u1E36\u1E38\u013B\u1E3C\u1E3A\u0141\u023D\u2C62\u2C60\uA748\uA746\uA780'},
{'base':'LJ','letters':'\u01C7'},
{'base':'Lj','letters':'\u01C8'},
{'base':'M', 'letters':'\u004D\u24C2\uFF2D\u1E3E\u1E40\u1E42\u2C6E\u019C'},
{'base':'N', 'letters':'\u004E\u24C3\uFF2E\u01F8\u0143\u00D1\u1E44\u0147\u1E46\u0145\u1E4A\u1E48\u0220\u019D\uA790\uA7A4'},
{'base':'NJ','letters':'\u01CA'},
{'base':'Nj','letters':'\u01CB'},
{'base':'O', 'letters':'\u004F\u24C4\uFF2F\u00D2\u00D3\u00D4\u1ED2\u1ED0\u1ED6\u1ED4\u00D5\u1E4C\u022C\u1E4E\u014C\u1E50\u1E52\u014E\u022E\u0230\u00D6\u022A\u1ECE\u0150\u01D1\u020C\u020E\u01A0\u1EDC\u1EDA\u1EE0\u1EDE\u1EE2\u1ECC\u1ED8\u01EA\u01EC\u00D8\u01FE\u0186\u019F\uA74A\uA74C'},
{'base':'OI','letters':'\u01A2'},
{'base':'OO','letters':'\uA74E'},
{'base':'OU','letters':'\u0222'},
{'base':'OE','letters':'\u008C\u0152'},
{'base':'oe','letters':'\u009C\u0153'},
{'base':'P', 'letters':'\u0050\u24C5\uFF30\u1E54\u1E56\u01A4\u2C63\uA750\uA752\uA754'},
{'base':'Q', 'letters':'\u0051\u24C6\uFF31\uA756\uA758\u024A'},
{'base':'R', 'letters':'\u0052\u24C7\uFF32\u0154\u1E58\u0158\u0210\u0212\u1E5A\u1E5C\u0156\u1E5E\u024C\u2C64\uA75A\uA7A6\uA782'},
{'base':'S', 'letters':'\u0053\u24C8\uFF33\u1E9E\u015A\u1E64\u015C\u1E60\u0160\u1E66\u1E62\u1E68\u0218\u015E\u2C7E\uA7A8\uA784'},
{'base':'T', 'letters':'\u0054\u24C9\uFF34\u1E6A\u0164\u1E6C\u021A\u0162\u1E70\u1E6E\u0166\u01AC\u01AE\u023E\uA786'},
{'base':'TZ','letters':'\uA728'},
{'base':'U', 'letters':'\u0055\u24CA\uFF35\u00D9\u00DA\u00DB\u0168\u1E78\u016A\u1E7A\u016C\u00DC\u01DB\u01D7\u01D5\u01D9\u1EE6\u016E\u0170\u01D3\u0214\u0216\u01AF\u1EEA\u1EE8\u1EEE\u1EEC\u1EF0\u1EE4\u1E72\u0172\u1E76\u1E74\u0244'},
{'base':'V', 'letters':'\u0056\u24CB\uFF36\u1E7C\u1E7E\u01B2\uA75E\u0245'},
{'base':'VY','letters':'\uA760'},
{'base':'W', 'letters':'\u0057\u24CC\uFF37\u1E80\u1E82\u0174\u1E86\u1E84\u1E88\u2C72'},
{'base':'X', 'letters':'\u0058\u24CD\uFF38\u1E8A\u1E8C'},
{'base':'Y', 'letters':'\u0059\u24CE\uFF39\u1EF2\u00DD\u0176\u1EF8\u0232\u1E8E\u0178\u1EF6\u1EF4\u01B3\u024E\u1EFE'},
{'base':'Z', 'letters':'\u005A\u24CF\uFF3A\u0179\u1E90\u017B\u017D\u1E92\u1E94\u01B5\u0224\u2C7F\u2C6B\uA762'},
{'base':'a', 'letters':'\u0061\u24D0\uFF41\u1E9A\u00E0\u00E1\u00E2\u1EA7\u1EA5\u1EAB\u1EA9\u00E3\u0101\u0103\u1EB1\u1EAF\u1EB5\u1EB3\u0227\u01E1\u00E4\u01DF\u1EA3\u00E5\u01FB\u01CE\u0201\u0203\u1EA1\u1EAD\u1EB7\u1E01\u0105\u2C65\u0250'},
{'base':'aa','letters':'\uA733'},
{'base':'ae','letters':'\u00E6\u01FD\u01E3'},
{'base':'ao','letters':'\uA735'},
{'base':'au','letters':'\uA737'},
{'base':'av','letters':'\uA739\uA73B'},
{'base':'ay','letters':'\uA73D'},
{'base':'b', 'letters':'\u0062\u24D1\uFF42\u1E03\u1E05\u1E07\u0180\u0183\u0253'},
{'base':'c', 'letters':'\u0063\u24D2\uFF43\u0107\u0109\u010B\u010D\u00E7\u1E09\u0188\u023C\uA73F\u2184'},
{'base':'d', 'letters':'\u0064\u24D3\uFF44\u1E0B\u010F\u1E0D\u1E11\u1E13\u1E0F\u0111\u018C\u0256\u0257\uA77A'},
{'base':'dz','letters':'\u01F3\u01C6'},
{'base':'e', 'letters':'\u0065\u24D4\uFF45\u00E8\u00E9\u00EA\u1EC1\u1EBF\u1EC5\u1EC3\u1EBD\u0113\u1E15\u1E17\u0115\u0117\u00EB\u1EBB\u011B\u0205\u0207\u1EB9\u1EC7\u0229\u1E1D\u0119\u1E19\u1E1B\u0247\u025B\u01DD'},
{'base':'f', 'letters':'\u0066\u24D5\uFF46\u1E1F\u0192\uA77C'},
{'base':'g', 'letters':'\u0067\u24D6\uFF47\u01F5\u011D\u1E21\u011F\u0121\u01E7\u0123\u01E5\u0260\uA7A1\u1D79\uA77F'},
{'base':'h', 'letters':'\u0068\u24D7\uFF48\u0125\u1E23\u1E27\u021F\u1E25\u1E29\u1E2B\u1E96\u0127\u2C68\u2C76\u0265'},
{'base':'hv','letters':'\u0195'},
{'base':'i', 'letters':'\u0069\u24D8\uFF49\u00EC\u00ED\u00EE\u0129\u012B\u012D\u00EF\u1E2F\u1EC9\u01D0\u0209\u020B\u1ECB\u012F\u1E2D\u0268\u0131'},
{'base':'j', 'letters':'\u006A\u24D9\uFF4A\u0135\u01F0\u0249'},
{'base':'k', 'letters':'\u006B\u24DA\uFF4B\u1E31\u01E9\u1E33\u0137\u1E35\u0199\u2C6A\uA741\uA743\uA745\uA7A3'},
{'base':'l', 'letters':'\u006C\u24DB\uFF4C\u0140\u013A\u013E\u1E37\u1E39\u013C\u1E3D\u1E3B\u017F\u0142\u019A\u026B\u2C61\uA749\uA781\uA747'},
{'base':'lj','letters':'\u01C9'},
{'base':'m', 'letters':'\u006D\u24DC\uFF4D\u1E3F\u1E41\u1E43\u0271\u026F'},
{'base':'n', 'letters':'\u006E\u24DD\uFF4E\u01F9\u0144\u00F1\u1E45\u0148\u1E47\u0146\u1E4B\u1E49\u019E\u0272\u0149\uA791\uA7A5'},
{'base':'nj','letters':'\u01CC'},
{'base':'o', 'letters':'\u006F\u24DE\uFF4F\u00F2\u00F3\u00F4\u1ED3\u1ED1\u1ED7\u1ED5\u00F5\u1E4D\u022D\u1E4F\u014D\u1E51\u1E53\u014F\u022F\u0231\u00F6\u022B\u1ECF\u0151\u01D2\u020D\u020F\u01A1\u1EDD\u1EDB\u1EE1\u1EDF\u1EE3\u1ECD\u1ED9\u01EB\u01ED\u00F8\u01FF\u0254\uA74B\uA74D\u0275'},
{'base':'oi','letters':'\u01A3'},
{'base':'ou','letters':'\u0223'},
{'base':'oo','letters':'\uA74F'},
{'base':'p','letters':'\u0070\u24DF\uFF50\u1E55\u1E57\u01A5\u1D7D\uA751\uA753\uA755'},
{'base':'q','letters':'\u0071\u24E0\uFF51\u024B\uA757\uA759'},
{'base':'r','letters':'\u0072\u24E1\uFF52\u0155\u1E59\u0159\u0211\u0213\u1E5B\u1E5D\u0157\u1E5F\u024D\u027D\uA75B\uA7A7\uA783'},
{'base':'s','letters':'\u0073\u24E2\uFF53\u00DF\u015B\u1E65\u015D\u1E61\u0161\u1E67\u1E63\u1E69\u0219\u015F\u023F\uA7A9\uA785\u1E9B'},
{'base':'t','letters':'\u0074\u24E3\uFF54\u1E6B\u1E97\u0165\u1E6D\u021B\u0163\u1E71\u1E6F\u0167\u01AD\u0288\u2C66\uA787'},
{'base':'tz','letters':'\uA729'},
{'base':'u','letters': '\u0075\u24E4\uFF55\u00F9\u00FA\u00FB\u0169\u1E79\u016B\u1E7B\u016D\u00FC\u01DC\u01D8\u01D6\u01DA\u1EE7\u016F\u0171\u01D4\u0215\u0217\u01B0\u1EEB\u1EE9\u1EEF\u1EED\u1EF1\u1EE5\u1E73\u0173\u1E77\u1E75\u0289'},
{'base':'v','letters':'\u0076\u24E5\uFF56\u1E7D\u1E7F\u028B\uA75F\u028C'},
{'base':'vy','letters':'\uA761'},
{'base':'w','letters':'\u0077\u24E6\uFF57\u1E81\u1E83\u0175\u1E87\u1E85\u1E98\u1E89\u2C73'},
{'base':'x','letters':'\u0078\u24E7\uFF58\u1E8B\u1E8D'},
{'base':'y','letters':'\u0079\u24E8\uFF59\u1EF3\u00FD\u0177\u1EF9\u0233\u1E8F\u00FF\u1EF7\u1E99\u1EF5\u01B4\u024F\u1EFF'},
{'base':'z','letters':'\u007A\u24E9\uFF5A\u017A\u1E91\u017C\u017E\u1E93\u1E95\u01B6\u0225\u0240\u2C6C\uA763'}
];
var diacriticsMap = {};
for (var i=0; i < defaultDiacriticsRemovalap.length; i++){
var letters = defaultDiacriticsRemovalap[i].letters.split("");
for (var j=0; j < letters.length ; j++){
diacriticsMap[letters[j]] = defaultDiacriticsRemovalap[i].base;
}
}
function removeDiacriticFromChar (char) {
return diacriticsMap[char] || char;
}
/*
* [1] Remove the accent, based on answer of /programming/990904/javascript-remove-accents-in-strings
* [2] Check if a to z character, using regex or unicode (your choice, here using regex)
*
*/
function isLetter(char) {
var charWithoutAccent = removeDiacriticFromChar(char); /* [1] */
return charWithoutAccent.match(/[a-z]/i); /* [2] */
}
console.log( "is 'u' is a letter? " + (isLetter('u') ? 'true' : 'false') );
console.log( "is 'ü' is a letter? " + (isLetter('ü') ? 'true' : 'false') );
console.log( "is 'à' is a letter? " + (isLetter('à') ? 'true' : 'false') );
console.log( "is 'ö' is a letter? " + (isLetter('ö') ? 'true' : 'false') );
console.log( "is 'ù' is a letter? " + (isLetter('ù') ? 'true' : 'false') );
console.log( "is 'é' is a letter? " + (isLetter('é') ? 'true' : 'false') );
console.log( "is 'é' is a letter? " + (isLetter('é') ? 'true' : 'false') );
console.log( "is 'ê' is a letter? " + (isLetter('ê') ? 'true' : 'false') );
我在这里发布是因为我不想发布新问题。假设代码中没有任何单个字符声明,则可以eval()引起错误并检查字符的类型。就像是:
function testForLetter(character) {
try {
//Variable declarations can't start with digits or operators
//If no error is thrown check for dollar or underscore. Those are the only nonletter characters that are allowed as identifiers
eval("let " + character + ";");
let regExSpecial = /[^\$_]/;
return regExSpecial.test(character);
} catch (error) {
return false;
}
}
console.log(testForLetter("!")); //returns false;
console.log(testForLetter("5")); //returns false;
console.log(testForLetter("ن")); //returns true;
console.log(testForLetter("_")); //returns false;
通过使用ES6中的标准内置函数isNaN或Number.isNaN(),可以知道字符是否为字母:
isNaN('s') // true
isNaN('-') // true
isNaN('32') // false, '32' is converted to the number 32 which is not NaN
如果给定值不是数字,则重新运行true,否则返回false。
// to check if the given string contain alphabets
function isPangram(sentence){
let lowerCased = sentence.toLowerCase();
let letters = "abcdefghijklmnopqrstuvwxyz";
// traditional for loop can also be used
for (let char of letters){
if (!lowerCased.includes(char)) return false;
}
return true;
}
我做了一个函数来做到这一点:
var isLetter = function (character) {
if( (character.charCodeAt() >= 65 && character.charCodeAt() <= 90) || (character.charCodeAt() >= 97 && character.charCodeAt() <= 122) ) {
return true;
}
else{
return false;
}
}
如果字符的代码引用字母,则基本上可以在ASCII表中进行验证。
您可以在此链接上看到ASCII表,并比较DEC列(代码在此处)和符号:https : //www.ascii-code.com/
注意:我的函数仅对“简单”字母(例如“Á”,“é”,“ç”,“Ü”)正确,它将返回false ...但是如果需要,您可以使此函数适应其他条件)。
NaN
?还是isNan(first)
我猜。