SOURCE

function writeDocument(variable) {
    document.write(variable + "<br/>");
} 
//数组
var arr = ["HTML","CSS","JavaScript","jQuery","Vue.js"];
writeDocument(arr[2]);
writeDocument(arr);
arr[4]="React.js";
writeDocument(arr);
arr[5]="Vue.js";
writeDocument(arr);
arr[8]="Angular.js";
writeDocument(arr);

//获取数组长度
var arr=["小羊真可爱","yangyangyang","zhangzhangzhang"];
writeDocument(arr);
writeDocument(arr.length);
writeDocument(arr.slice(0,3));
writeDocument(arr.push(1,2,3));
writeDocument(arr.unshift("啦啦啦"));
writeDocument(arr.shift(1));
writeDocument(arr.pop(2));

writeDocument("升降序排序......***...........");
 //定义一个升序函数
        function up(a, b) 
        {
            return a - b;
        }
        //定义一个降序函数
        function down(a, b) 
        {
            return b - a;
        }
        //定义数组
        var arr = [3, 9, 1, 12, 50, 21];
        arr.sort(up);
        document.write("升序：" + arr.join("、") + "<br/>");
        arr.sort(down);
        document.write("降序：" + arr.join("、")+ "<br/>");
var str1 = "绿叶学习网";
var str2 = str1.split("").join("><");
var arr = str2.split("");
arr.unshift("<");
arr.push(">");
var result = arr.join("");
document.write(result);