我想打印数组的最后一个'n'元素 [英] I want to print the last 'n' elements of an array

问题描述

我正在编写一个JavaScript函数来获取数组的最后n个元素.如果array有6个元素，而用户给出4，则必须返回最后4个元素.如果用户给出的"n"大于数组中元素的数量，则它应返回所有元素.

I am writing a JavaScript function to get the last 'n' elements of the array. If array has 6 elements and if user gives 4, it has to return last 4 elements. If user gives ‘n’ which is greater than the number of elements in the array, then it should return all elements.

问题是，如果数组有8个元素并且我给出数字10，结果是:undefined undefined 1 2 3 4 5 6 7 8

The problem is if If the array has 8 elements and I give number 10. The result is : undefined undefined 1 2 3 4 5 6 7 8

我只想显示不带"undefined"的数字.

I want to display only the numbers without "undefined".

谢谢

HTML代码

该数组是:

1,2,3,4,5,6,7,8

        <br>
        x:
        <input type="number" id="x" value="2" >
        <br>
        <button onclick="elements()"> Get the elements </button>

        <p id="result"></p>

    <script src="ex10.js"></script>

JavaScript代码

JavaScript code

 var Elements = new Array(1,2,3,4,5,6,7,8);

    function elements(){
    var x = document.getElementById("x").value;

    for(var i=Elements.length - x; i <=Elements.length-1; i++)
    {
    document.getElementById("result").innerHTML += Elements[i] + " ";
    }

}

推荐答案

您可以将slice从末尾算起.然后join元素用于格式化输出.

You could take slice with a negative count from the end. Then join the elements for a formatted output.

一些链接:

• Array#slice
• Array#join

var array = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(array.slice(-4).join(' '));

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