SOURCE

function writeDocument(variable){

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

var welcomeString="welcome"

writeDocument(welcomeString+'<br/>'); 

writeDocument(welcomeString.length+'<br/>'); //获取字符串长度

//大小写转换
writeDocument(welcomeString.toLowerCase()+'<br/>');
writeDocument(welcomeString.toUpperCase()+'<br/>');
writeDocument("-------------------------------");

//获取指定位置字符
writeDocument(welcomeString.charAt(2));

//截取字符串
writeDocument(welcomeString.substring(3));
writeDocument(welcomeString.substring(0,2));

//替换字符
//字符串名.replace(原字符串, 替换字符串)：只会替换第一个字符
//字符串名.replace(正则表达式, 替换字符串)：全部替换
var sentence="we have fun in our class,we are happy"
writeDocument(sentence);
writeDocument(sentence.replace("we","You"));
writeDocument(sentence.replace(/class/g,"programming class"));
writeDocument("-------------------------------");

//分割字符
var splitSentence="We have fun in our class"
writeDocument(splitSentence);
writeDocument(splitSentence.split(" "));
writeDocument(welcomeString);
writeDocument(welcomeString.split(""));  //用英文逗号作为分割符

writeDocument("-------------------------------");

//查找字符的位置
//indexOf()找出“某个指定字符串”在字符串中首次出现的下标位置,若找不到该字符串，则返回-1;
//lastIndexOf()找出“某个指定字符串”在字符串中最后出现的下标位置
writeDocument(sentence.indexOf("class"));
writeDocument(sentence.lastIndexOf("class"));
writeDocument(sentence.match(/class/g));
writeDocument(sentence.search(/class/g));

writeDocument("-------------------------------");

//统计字符个数
function szq(str,char){
    var num = 0;
    for(var i=0;i<str.length;i++)
    {
        var char = str.charAt(i);
        
        //将每一个字符转换为小写，然后判断是否与“c”相等
        if (char.toLowerCase() == "c")
        {
            num += 1;
        }
    }
    return num;
}

//var str="Can you can a can as a Canner can can a can";
writeDocument("字符串中含有c的个数为:"+szq("Can you can a can as a Canner can can a can"));

writeDocument("-------------------------------");

//统计字符串中的数字
function countNum(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;
}
    writeDocument("字符串中的数字个数为:"+countNum("2df35g6g"));