JavaScript实现数组元素增减的方法示例

var numberArray = [12,23,34,45];
numberArray[numberArray.length] = 56;
console.log(numberArray);//输出[12,23,34,45,56]

//利用push()方法在数组尾部添加元素
var numberArray = [12,23,34,45];
var newLength = numberArray.push(56);
console.log(newLength);//输出5
console.log(numberArray);//输出[12,23,34,45,56]

var sArray = ["ja","va","script"];
var newLength = sArray.unshift("he","llo");
console.log(newLength)//输出5
console.log(sArray);//输出["he","llo","ja","va","script"];

var array = [1,2,true,"hello"];
array.length = 3;//索引最大的元素被删除
console.log(array);//输出[1,2,true]

var dArray = [11,22,33,44,55];
delete dArray[4];//删除索引最大的元素
console.log(dArray);//输出[11,22,33,44]
console.log(dArray.length); //长度为5

//利用pop()方法在数组尾部删除元素
var numberArray = [3,4,5,6,7];
var deletedNumber = numberArray.pop();
console.log(deletedNumber);//输出被删除的元素7
console.log(numberArray);//删除后的数组为[3,4,5,6]

var dArray = [11,22,33,44,55];
console.log(dArray.shift());//输出11，11被从数组中删除
console.log(dArray);//输出[22,33,44,55]

var testArray = [12,"java","js","c","c++",24,36,"python","c#","css"];
function mainJs(a,b) {
    a = parseInt(a);
    b = parseInt(b);
    //请在此处编写代码
    /*********begin*********/
    for (var i = 1; i <= a; i++){
        testArray.unshift(testArray.pop());
    }
    return testArray[b];
    /*********end*********/
}