SOURCE

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

document.write("//---chatAt-----------------------------<br/>");
document.write(welcomeString.charAt(2)+"<br/>");
document.write(welcomeString.charAt(6)+"<br/>");

document.write("//---substring-----------------------------<br/>");
document.write(welcomeString.substring(3)+"<br/>");
document.write(welcomeString.substring(0,2)+"<br/>");

document.write("//---replace-----------------------------<br/>");
var sentence="we have fun in our clsss"
document.write(welcomeString.replace()+"<br/>");
document.write(welcomeString.replace()+"<br/>");

document.write("//------replace-----------------<br/>");
var sentence="We have fun in our class,Do you have fun in your class?"
document.write(sentence);
document.write(sentence.replace("class","programming class")+"<br/>");
document.write(sentence.replace(/class/g,"programming class"+"<br/>"));

document.write("//------split----------------------<br/>");
document.write(sentence.split(" ")+"<br/>");
document.write(welcomeString.split("")+"<br/>");
document.write(sentence.split(".")+"<br/>");

document.write("//--------indexOf--------------------<br/>");
document.write(sentence.indexOf("class")+"<br/>");
document.write(sentence.lastIndexOf("class")+"<br/>");
document.write(sentence.match("class")+"<br/>");
document.write(sentence.match(/class/g)+"<br/>");
document.write(sentence.search(/class/g)+"<br/>");

//判断统计某一个字符的个数
function countChar(stringToCount, char) {
    var charCount = 0;
for(var i=0;i<stringToCount.length;i++)
        {
            var a = stringToCount.charAt(i);
            //将每一个字符转换为小写，然后判断是否与“c”相等
            if (a.toLowerCase() == char) {
                charCount += 1;
            }
        }
    return charCount;
}
var stringToCount = "Can you can a can as a Canner can can a can";
document.write("There are " + countChar(stringToCount, "c") + " c in " + stringToCount+"<br/>"); 

function getNum(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;
        }
        document.write(getNum("1w2e3r4t5gg")+"<br/>");