使用JavaScript将字符串转换为标题大小写

没有使用正则表达式，仅供参考：

String.prototype.toProperCase = function() {
  var words = this.split(' ');
  var results = [];
  for (var i = 0; i < words.length; i++) {
    var letter = words[i].charAt(0).toUpperCase();
    results.push(letter + words[i].slice(1));
  }
  return results.join(' ');
};

console.log(
  'john smith'.toProperCase()
)

如果您担心那些填充词语，您可以告诉函数不要大写它们。

/**
 * @param String str The text to be converted to titleCase.
 * @param Array glue the words to leave in lowercase. 
 */
var titleCase = function(str, glue){
    glue = (glue) ? glue : ['of', 'for', 'and'];
    return str.replace(/(\w)(\w*)/g, function(_, i, r){
        var j = i.toUpperCase() + (r != null ? r : "");
        return (glue.indexOf(j.toLowerCase())<0)?j:j.toLowerCase();
    });
};

希望这对你有所帮助。

编辑

如果你想处理前导词，可以用一个额外的变量来跟踪：

var titleCase = function(str, glue){
    glue = !!glue ? glue : ['of', 'for', 'and', 'a'];
    var first = true;
    return str.replace(/(\w)(\w*)/g, function(_, i, r) {
        var j = i.toUpperCase() + (r != null ? r : '').toLowerCase();
        var result = ((glue.indexOf(j.toLowerCase()) < 0) || first) ? j : j.toLowerCase();
        first = false;
        return result;
    });
};

如果您需要一份语法正确的答案：

这个答案考虑到介词，如“of”，“from”等，会生成一个你在论文中期望看到的编辑风格标题。

toTitleCase 函数

该函数考虑到语法规则（在此列出）。该函数还合并空白并删除特殊字符（根据您的需求修改正则表达式）。

const toTitleCase = (str) => {
  const articles = ['a', 'an', 'the'];
  const conjunctions = ['for', 'and', 'nor', 'but', 'or', 'yet', 'so'];
  const prepositions = [
    'with', 'at', 'from', 'into','upon', 'of', 'to', 'in', 'for',
    'on', 'by', 'like', 'over', 'plus', 'but', 'up', 'down', 'off', 'near'
  ];

  // The list of spacial characters can be tweaked here
  const replaceCharsWithSpace = (str) => str.replace(/[^0-9a-z&/\\]/gi, ' ').replace(/(\s\s+)/gi, ' ');
  const capitalizeFirstLetter = (str) => str.charAt(0).toUpperCase() + str.substr(1);
  const normalizeStr = (str) => str.toLowerCase().trim();
  const shouldCapitalize = (word, fullWordList, posWithinStr) => {
    if ((posWithinStr == 0) || (posWithinStr == fullWordList.length - 1)) {
      return true;
    }

    return !(articles.includes(word) || conjunctions.includes(word) || prepositions.includes(word));
  }

  str = replaceCharsWithSpace(str);
  str = normalizeStr(str);

  let words = str.split(' ');
  if (words.length <= 2) { // Strings less than 3 words long should always have first words capitalized
    words = words.map(w => capitalizeFirstLetter(w));
  }
  else {
    for (let i = 0; i < words.length; i++) {
      words[i] = (shouldCapitalize(words[i], words, i) ? capitalizeFirstLetter(words[i], words, i) : words[i]);
    }
  }

  return words.join(' ');
}

单元测试确保正确性

import { expect } from 'chai';
import { toTitleCase } from '../../src/lib/stringHelper';

describe('toTitleCase', () => {
  it('Capitalizes first letter of each word irrespective of articles, conjunctions or prepositions if string is no greater than two words long', function(){
    expect(toTitleCase('the dog')).to.equal('The Dog'); // Capitalize articles when only two words long
    expect(toTitleCase('for all')).to.equal('For All'); // Capitalize conjunctions when only two words long
    expect(toTitleCase('with cats')).to.equal('With Cats'); // Capitalize prepositions when only two words long
  });

  it('Always capitalize first and last words in a string irrespective of articles, conjunctions or prepositions', function(){
    expect(toTitleCase('the beautiful dog')).to.equal('The Beautiful Dog');
    expect(toTitleCase('for all the deadly ninjas, be it so')).to.equal('For All the Deadly Ninjas Be It So');
    expect(toTitleCase('with cats and dogs we are near')).to.equal('With Cats and Dogs We Are Near');
  });

  it('Replace special characters with space', function(){
    expect(toTitleCase('[wolves & lions]: be careful')).to.equal('Wolves & Lions Be Careful');
    expect(toTitleCase('wolves & lions, be careful')).to.equal('Wolves & Lions Be Careful');
  });

  it('Trim whitespace at beginning and end', function(){
    expect(toTitleCase(' mario & Luigi superstar saga ')).to.equal('Mario & Luigi Superstar Saga');
  });

  it('articles, conjunctions and prepositions should not be capitalized in strings of 3+ words', function(){
    expect(toTitleCase('The wolf and the lion: a tale of two like animals')).to.equal('The Wolf and the Lion a Tale of Two like Animals');
    expect(toTitleCase('the  three Musketeers  And plus ')).to.equal('The Three Musketeers and Plus');
  });
});

如果上面的解决方案中使用的正则表达式让你感到困惑，试试这段代码：

function titleCase(str) {
  return str.split(' ').map(function(val){ 
    return val.charAt(0).toUpperCase() + val.substr(1).toLowerCase();
  }).join(' ');
}

我创建了这个函数，可以处理姓氏（所以不是标题大小写）例如“McDonald”或“MacDonald”或“O'Toole”或“D'Orazio”。但它并不能处理德语或荷兰语中通常用小写书写的“van”或“von”等姓氏... 我相信“de”也经常用小写表示，比如“Robert de Niro”。这些仍需要解决。

function toProperCase(s)
{
  return s.toLowerCase().replace( /\b((m)(a?c))?(\w)/g,
          function($1, $2, $3, $4, $5) { if($2){return $3.toUpperCase()+$4+$5.toUpperCase();} return $1.toUpperCase(); });
}

如果您可以在代码中使用第三方库，那么lodash为我们提供了一个助手函数。

https://lodash.com/docs/4.17.3#startCase

_.startCase('foo bar');
// => 'Foo Bar'

_.startCase('--foo-bar--');
// => 'Foo Bar'
 
_.startCase('fooBar');
// => 'Foo Bar'
 
_.startCase('__FOO_BAR__');
// => 'FOO BAR'

首先，通过使用空格拆分字符串将其转换为数组：

var words = str.split(' ');

然后使用array.map创建一个新数组，其中包含首字母大写的单词。

var capitalized = words.map(function(word) {
    return word.charAt(0).toUpperCase() + word.substring(1, word.length);
});

然后使用join函数将新数组按空格连接：

capitalized.join(" ");

function titleCase(str) {
  str = str.toLowerCase(); //ensure the HeLlo will become Hello at the end
  var words = str.split(" ");

  var capitalized = words.map(function(word) {
    return word.charAt(0).toUpperCase() + word.substring(1, word.length);
  });
  return capitalized.join(" ");
}

console.log(titleCase("I'm a little tea pot"));

注意：

这种方法有一个缺点，它只会将每个单词的首字母大写。在这里，“单词”指的是由空格分隔的每个字符串。

假设您有以下字符串：

str = "I'm a little/small tea pot";

使用此方法会产生：

I'm A Little/small Tea Pot

与期望的结果不符：

I'm A Little/Small Tea Pot

在这种情况下，可以使用正则表达式和.replace方法来解决问题：

使用ES6语法：

const capitalize = str => str.length
  ? str[0].toUpperCase() +
    str.slice(1).toLowerCase()
  : '';

const escape = str => str.replace(/./g, c => `\\${c}`);
const titleCase = (sentence, seps = ' _-/') => {
  let wordPattern = new RegExp(`[^${escape(seps)}]+`, 'g');
  
  return sentence.replace(wordPattern, capitalize);
};
console.log( titleCase("I'm a little/small tea pot.") );

或者不使用ES6：

function capitalize(str) {
  return str.charAt(0).toUpperCase() + str.substring(1, str.length).toLowerCase();
}

function titleCase(str) {
  return str.replace(/[^\ \/\-\_]+/g, capitalize);
}

console.log(titleCase("I'm a little/small tea pot."));

ES 6

str.split(' ')
   .map(s => s.slice(0, 1).toUpperCase() + s.slice(1).toLowerCase())
   .join(' ')

否则

str.split(' ').map(function (s) {
    return s.slice(0, 1).toUpperCase() + s.slice(1).toLowerCase();
}).join(' ')

function toTitleCase(str)
{
    return str.replace(/\b\w/g, function (txt) { return txt.toUpperCase(); });
}

对于像Jim-Bob这样的连字符姓名也适用。

尝试一下这个，最简单的方法：

str.replace(/(^[a-z])|(\s+[a-z])/g, txt => txt.toUpperCase());