SOURCE

function writeDocument(variable) {
    document.write(variable + "<br/>");
}
var str1 = "Comeonforyou!";
document.write("字符串长度是：" + str1.length + "<br/>");
document.write("小写：" + str1.toLowerCase() + "<br/>");
document.write("大写：" + str1.toUpperCase() + "<br/>");
document.write("第1个字符是：" + str1.charAt(0) + "<br/>");
document.write("第5个字符是：" + str1.charAt(6) + "<br/>");
var str2 = str1.substring(2, 5);
document.write(str2 + "<br/>");

var str = "I am iron man,don't forget it,over.";
document.write(str.replace("am", "hero" + "<br/>"));
document.write(str.replace(/iron/g, "hero" + "<br/>"));

var str = "I get it";
var arr1 = str.split(" ");//有空格
document.write("数组第1个元素是：" + arr1[0] + "<br/>");
document.write("数组第2个元素是：" + arr1[1] + "<br/>");
document.write("数组第3个元素是：" + arr1[2] + "<br/>");

var arr2 = str.split("");//无空格
document.write("数组第1个元素是：" + arr2[0] + "<br/>");
document.write("数组第2个元素是：" + arr2[1] + "<br/>");
document.write("数组第3个元素是：" + arr2[2] + "<br/>");
document.write("数组第4个元素是：" + arr2[3] + "<br/>");

var str = "The world jojo!";
document.write(str.indexOf("hh") + "<br/>");
document.write(str.indexOf("world") + "<br/>");
document.write(str.indexOf("jojo") + "<br/>");
document.write("e首次出现的下标是：" + str.indexOf("e") + "<br/>");
document.write("e最后出现的下标是：" + str.lastIndexOf("e") + "<br/>");


var str = "Can you can a can as a Canner can can a can";
function countChar(str, char) {
    var charCount = 0;
    for (var i = 0; i < str.length; i++) {
        var char = str.charAt(i);
        //将每一个字符转换为小写，然后判断是否与“c”相等
        if (char.toLowerCase() == "c") {
            charCount += 1;
        }
    }
    return charCount;
}

writeDocument("There are " + countChar(str, "c") + " c in " + str);


//统计字符串中有多少个数字？
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("12gfc5d"));