SOURCE

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



var welComeString="welcome";

writeDocument(welComeString);
writeDocument(welComeString.length);
writeDocument(welComeString.toLowerCase());
writeDocument(welComeString.toUpperCase());
writeDocument(welComeString.charAt(2));
writeDocument(welComeString.charAt(6));
writeDocument(welComeString.substring(3));
writeDocument(welComeString.substring(0,2));

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

var splitSentence="We have fun in our class. ";
writeDocument(splitSentence);
writeDocument(splitSentence.split(" "));//把单词分割
writeDocument(welComeString);//
writeDocument(welComeString.split(""));//把字母分割
writeDocument(sentence.split(""));//把句子分割
writeDocument("//Indexof--------------------------------------------------------");
writeDocument(sentence.indexOf("class"));//若找不到，返回-1；
writeDocument(sentence.lastIndexOf("class"));
writeDocument(sentence.match("class"));
writeDocument(sentence.match(/class/g));
writeDocument(sentence.search(/class/g));


//如何找出字符串“Can you can a can as a Canner can can a can”中找出所有c的个数，不区分大小写。
function countChar(stringValue,char){
    var charCount=0;

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


function co(s,c){
    var cc=0;
    for(var i=0;i<s.length;i++){
        if(s.charAt(i).toLowerCase()==c){
            ++cc;
        }
       
    } 
    return cc;
}
var s="bananan nanana";
writeDocument("there are"+co(s,"a"));