SOURCE

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

document.write("//---case------------------------------");
var welcomeString=("Welcome");
document.write(welcomeString+"</br>");
document.write(welcomeString.length+"</br>");
document.write(welcomeString.toUpperCase()+"</br>");
document.write(welcomeString.toLowerCase()+"</br>");

writeDocument("//---charAt------------------------------");
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 our 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(sentence.split(""));
writeDocument(sentence.split("."));

writeDocument("//---indexOf/lastIndexOf/match/search------------");
writeDocument(sentence.indexOf("class"));
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(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); 


writeDocument("//--------------------------------------------------");
/*给大家一个任意字符串，然后统计一下里面有多少个数字。使用for循环
结合charAt()方法来获取字符串中的每一个字符，然后判断该字符是否是数字*/
function countNumber(stringtoCount,num) {

    var numCount = 0;
    for(var i=0;i<stringtoCount.length;i++){
        if(stringtoCount.charAt(i)>='0' && stringtoCount.charAt(i) <= '9'){
             numCount++;
             writeDocument(stringtoCount.charAt(i)+"是数字");
        }
        else{
             writeDocument(stringtoCount.charAt(i)+"不是数字");
        }
    }

     return numCount;

}
isNaN("sc99w7i4djh3");
var stringtoCount="sc99w7i4djh3";
writeDocument("有"+countNumber(stringtoCount)+"个数字在字符串中");