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

var sentence="i am happy.what about i? happy?"
writeDocument(sentence);
//原字符串
writeDocument(sentence.replace("i","u"));
//正则表达式
writeDocument(sentence.replace(/i/g,"u"));
writeDocument("=============================");

var splitSentence="you are pretty~";
//空格分隔符
writeDocument(splitSentence);
writeDocument(splitSentence.split(" "));
//空字符串切割
writeDocument(welcomeString);
writeDocument(welcomeString.split(""));
writeDocument("=============================");

writeDocument(sentence);
writeDocument(sentence.split(""));
writeDocument(sentence.split(" "));
writeDocument("=============================");

writeDocument(sentence.indexOf("happy"));
writeDocument(sentence.lastIndexOf("happy"));
writeDocument(sentence.match("happy"));
writeDocument(sentence.match(/happy/g));
//search只能用正则表达式
writeDocument(sentence.search(/happy/g));
writeDocument("=============================");


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("有"+countChar(stringValue,"c")+"个c在句子里");
writeDocument("=============================");

function countNumber(stringtoCount) {
    var numCount = 0;
    for (var f = 0; f < stringtoCount.length; f++) {
        var char = stringtoCount.charAt(f);
            if (char != " " && !isNaN(char)) {
                 numCount++;
            }
        }
    return numCount;
}
writeDocument("有"+countNumber("5kk2xx0rr")+"个数字在该字符串里");