SOURCE

function writeDoucument(variable){
    document.write(variable+"<br/>");
}
var welcomeString = "welcome!";
//case
document.write(welcomeString+"<br/>");
document.write(welcomeString.length+"<br/>");
document.write(welcomeString.toLowerCase()+"<br/>");
document.write(welcomeString.toUpperCase()+"<br/>");
//charAt
writeDoucument(welcomeString.charAt(3));
writeDoucument(welcomeString.charAt(4));
//substring
writeDoucument(welcomeString.substring(3));
writeDoucument(welcomeString.substring(0,2));
//replace
var setence = "we are family! are";
writeDoucument(setence);
writeDoucument(setence.replace("we","they"));
writeDoucument(setence.replace(/family/g,"cat"));
//split
var splitSetence = "i am happy";
writeDoucument(splitSetence);
writeDoucument(setence.split(" "));
writeDoucument(welcomeString);
writeDoucument(welcomeString.split(""));
writeDoucument(setence.split(""));
//indexOf
////setence中的第一个are
writeDoucument(setence.indexOf("are"));
//setence中的最后一个are
writeDoucument(setence.lastIndexOf("are"));
writeDoucument(splitSetence.match("am"));
writeDoucument(splitSetence.match(/am/g));
writeDoucument(splitSetence.search(/am/g));

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";
writeDoucument("There are"+countChar(stringValue,"c")+" in sentence.");

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("1d3sdsg"));