SOURCE

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

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);

writeDocument("获取数组长度-------------------------")
writeDocument(arr.length);
writeDocument("获取数组某一段-------------------------")
writeDocument(arr.slice(1,3));
writeDocument("往数组头添加元素-------------------------")
writeDocument(arr.unshift("web","technology"));
writeDocument(arr);
writeDocument("往数组尾部添加元素-------------------------")
writeDocument(arr.push("Bootstrap","Sass"));
writeDocument(arr);
writeDocument("删除数组头部元素-------------------------")
writeDocument(arr.shift());
writeDocument(arr);
writeDocument("删除数组尾部元素-------------------------")
writeDocument(arr.pop());
writeDocument(arr);

writeDocument("--------------------------------------------------------")

var numArr=[3,6,9,1,4,11]
writeDocument("排序前"+numArr)

function upcompare(l,r){
    if(l>r){
        return 1;
    }
    if(l==r){
        return 0;
    }
    if(l<r){
        return -1;
    }
}

numArr.sort(upcompare);
writeDocument("升序排序后"+numArr);

function downcompare(l,r){
    if(l>r){
        return -1;
    }
    if(l==r){
        return 0;
    }
    if(l<r){
        return 1;
    }
}

numArr.sort(downcompare);
writeDocument("降序排序后"+numArr);