SOURCE

function writeDocument(variable)
{
    document.write(variable + "<br/>");
} 

var welcomeString="Welcome";

writeDocument(welcomeString);
writeDocument(welcomeString.length);

writeDocument("//---case----------------");
writeDocument(welcomeString.toLowerCase());
writeDocument(welcomeString.toUpperCase());

writeDocument("//---chatAt----------------");
writeDocument(welcomeString.charAt(2));
writeDocument(welcomeString.charAt(6));

writeDocument("//---substring----------------");
writeDocument(welcomeString.substring(3));
writeDocument(welcomeString.substring(0,2));

writeDocument("//---replace----------------");
var sentence = "We have fun in our class. Do you have fun in your class?"
writeDocument(sentence);
writeDocument(sentence.replace("class","programming class"));
writeDocument(sentence.replace(/class/g,"programming class"));

writeDocument("//---split----------------");
writeDocument(sentence.split(" "));
writeDocument(welcomeString.split(""));

writeDocument("//---indexOf/lastIndexOf/match/search----------------");
writeDocument(sentence.indexOf("class"));//第一个出现的位置
writeDocument(sentence.lastIndexOf("class"));//最后出现的位置
writeDocument(sentence.match("class"));//有无出现单词
writeDocument(sentence.match(/class/g));//出现了几个
writeDocument(sentence.search(/class/g));//第一个

function countChar(stringToCount,char)
{
    var charCount = 0;
    for(var i = 0; i < stringToCount.length; ++i)
    {
        if(stringToCount.charAt(i.toLowerCase)==char)
        {
            ++charCount;
        }
    }
    return charCount;
}
var stringToCount = "Can you can a can as a Canner can can a can";
writeDocument("There are " + countChar(stringToCount, "c") + " c in " + stringToCount); 


function getNum(str)
{
    var num = 0;
    for (var i = 0; i < str.length; i++)
    {
        var char = str.charAt(i);
        //isNaN()对空格字符会转化为0，需要加个判断charAt(i)不能为空格
        if (char != " " && !isNaN(char))
        {
            num++;
        }
    }
    return num;
}
document.write(getNum("1d3sdsg"));