function toTitleCase(str) {
  var strnew = "";
  var i = 0;

  for (i = 0; i < str.length; i++) {
    if (i == 0) {
      strnew = strnew + str[i].toUpperCase();
    } else if (i != 0 && str[i - 1] == " ") {
      strnew = strnew + str[i].toUpperCase();
    } else {
      strnew = strnew + str[i];
    }
  }

  alert(strnew);
}

toTitleCase("hello world how are u");

这个解决方案将标点符号考虑到新句子中，处理引用，将小词转换为小写，忽略首字母缩写或全大写单词。

var stopWordsArray = new Array("a", "all", "am", "an", "and", "any", "are", "as", "at", "be", "but", "by", "can", "can't", "did", "didn't", "do", "does", "doesn't", "don't", "else", "for", "get", "gets", "go", "got", "had", "has", "he", "he's", "her", "here", "hers", "hi", "him", "his", "how", "i'd", "i'll", "i'm", "i've", "if", "in", "is", "isn't", "it", "it's", "its", "let", "let's", "may", "me", "my", "no", "of", "off", "on", "our", "ours", "she", "so", "than", "that", "that's", "thats", "the", "their", "theirs", "them", "then", "there", "there's", "these", "they", "they'd", "they'll", "they're", "they've", "this", "those", "to", "too", "try", "until", "us", "want", "wants", "was", "wasn't", "we", "we'd", "we'll", "we're", "we've", "well", "went", "were", "weren't", "what", "what's", "when", "where", "which", "who", "who's", "whose", "why", "will", "with", "won't", "would", "yes", "yet", "you", "you'd", "you'll", "you're", "you've", "your");

// Only significant words are transformed. Handles acronyms and punctuation
String.prototype.toTitleCase = function() {
    var newSentence = true;
    return this.split(/\s+/).map(function(word) {
        if (word == "") { return; }
        var canCapitalise = true;
        // Get the pos of the first alpha char (word might start with " or ')
        var firstAlphaCharPos = word.search(/\w/);
        // Check for uppercase char that is not the first char (might be acronym or all caps)
        if (word.search(/[A-Z]/) > 0) {
            canCapitalise = false;
        } else if (stopWordsArray.indexOf(word) != -1) {
            // Is a stop word and not a new sentence
            word.toLowerCase();
            if (!newSentence) {
                canCapitalise = false;
            }
        }
        // Is this the last word in a sentence?
        newSentence = (word.search(/[\.!\?:]['"]?$/) > 0)? true : false;
        return (canCapitalise)? word.replace(word[firstAlphaCharPos], word[firstAlphaCharPos].toUpperCase()) : word;
    }).join(' ');
}

// Pass a string using dot notation:
alert("A critical examination of Plato's view of the human nature".toTitleCase());
var str = "Ten years on: a study into the effectiveness of NCEA in New Zealand schools";
str.toTitleCase());
str = "\"Where to from here?\" the effectivness of eLearning in childhood education";
alert(str.toTitleCase());

/* Result:
A Critical Examination of Plato's View of the Human Nature.
Ten Years On: A Study Into the Effectiveness of NCEA in New Zealand Schools.
"Where to From Here?" The Effectivness of eLearning in Childhood Education. */

一种稍微优雅一点的方式，改编了Greg Dean的功能:

String.prototype.toProperCase = function () {
    return this.replace(/\w\S*/g, function(txt){return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase();});
};

这样称呼它:

"pascal".toProperCase();

如果你担心这些填充词，你可以告诉函数什么不大写。

/**
 * @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();
    });
};

希望这能帮到你。

edit

如果你想处理领先的粘合词，你可以跟踪这个w/另一个变量:

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;
    });
};

如果上述解决方案中使用的正则表达式让你感到困惑，试试下面的代码:

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

对于我们这些害怕正则表达式的人(lol):

函数标题案例（str） { var words = str.split（“ ”）; for （ var i = 0; i < words.length; i++ ） { var j = words[i].charAt（0）.toUpperCase（）; 单词[i] = j + words[i].substr（1）; } 返回 words.join（“ ”）; }