SOURCE

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

var str="welcome";
writeDocument(str.charAt(2));
writeDocument(str.charAt(6));
writeDocument(str.substring(3));
writeDocument(str.substring(0,2));

var sence="we have fun in class.Do you have fun in class";
writeDocument(sence);
writeDocument(sence.replace("have","had"));
writeDocument(sence.replace(/class/g,"there"));

var abbd="we have fun in class";
writeDocument(abbd);
writeDocument(abbd.split(""));
writeDocument(abbd.split(" "));
writeDocument(sence.split("."));

writeDocument(sence.indexOf("class"));
writeDocument(sence.lastIndexOf("class"));

var string="Can you can a can as a Canner can can a can";
function count(str,char)
{
    var s=0;
    for(var i=0;i<str.length;i++)
    {
        var ca=str.charAt(i);
        if(ca.toLowerCase()=="c")
        {
            s++;
        }
    }
    return s;
}
writeDocument(count(string,"c"));

function countNumber(stringtoCount) {
    var numCount = 0;
    
    for(var i=0;i<stringtoCount.length;i++){  
        if(isNaN(stringtoCount.substring(i,i+1))==false){
            numCount++
        }
    }
     return numCount;

}
var numC="zxc231sd2fe4dv2g"
document.write(numC+"<br>")
document.write("字符串中有"+countNumber(numC)+"个数字"+"<br>")