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

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("--------------------------------------")
var splitSentence = "we have fun in our class."
writeDocument(splitSentence);
writeDocument(splitSentence.split(" "));
writeDocument(welcomeString);
writeDocument(welcomeString.split(""));
writeDocument(sentence.split("."))
writeDocument("--------------------------------------")
writeDocument(sentence.indexOf("class"));
writeDocument(sentence.lastIndexOf("class"));
writeDocument(sentence.match("class"));
writeDocument(sentence.match(/class/g));
writeDocument(sentence.search(/class/g));

writeDocument("--------------------------------------")
var sen="can you can a can as a Canner can can a can"
sen=sen.toLowerCase();
function countChar(stringValue, char) {
    var count = 0;
    for(var i=0;i<sen.length;i++){
        if(stringValue.charAt(i)==char)
        {
            count++;
        }
    }
    return count;
}
writeDocument("该语句中c的个数为："+countChar(sen,"c"));

writeDocument("--------------------------------------")
var a="My QQ num is 310053938"
function countNum(string){
    var count=0;
    for(j=0;j<a.length;j++){
        var result=isNaN(a.charAt(j))
        if(result==false&&a.charAt(j)!=" "){
            count++;
        }
    }
    return count;
}
writeDocument("该语句中数字的个数为："+countNum(a));

var str = "Rome was not built in a day";  //定义字符串
var str = str.replace(/\s*/g,"");
var charCount = 0;

for (var ch of str) {

    charCount++;

}

writeDocument("该语句字符个数为："+charCount);