javascript 获取数组的最后一个值并将其显示在 X 轴下
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Getting the last value of an Array and showing it under X axis
提问by Headshota
var NewdateData[] = [1,2,3,4,5,6,7,8,9,1,2,1,23,45,56]
This NewdateDatais dynamically filled from database depending upon the selection made from the user interface.
这NewdateData是根据从用户界面所做的选择从数据库动态填充的。
I am using this NewdateDatafor displaying under the X axis Charts.
我使用它NewdateData在 X 轴图表下显示。
The issue I am facing is that, the values are not taken till the end , I want to have the last value to have under the X axis Labels.
我面临的问题是，直到最后才取值，我想在 X 轴标签下获得最后一个值。
xaxis: {tickFormatter: function(n)
{
var k = Math.round(n);
return NewdateData[k];
}
I am using flotr.
我正在使用flotr。
回答by Headshota
You can get the last value of an array with:
您可以使用以下命令获取数组的最后一个值：
NewdateData[NewdateData.length-1];
回答by Shawn Swanson
I don't have enough points to comment on Radman's post., but his solution is wrong.
我没有足够的分数来评论 Radman 的帖子。但他的解决方案是错误的。
let arr = [1, 2, 3, 4, 5]; let last = arr.slice(-1); // last = 5
让 arr = [1, 2, 3, 4, 5]; 让 last = arr.slice(-1); // 最后= 5
Returns [5], not 5.
返回 [5]，而不是 5。
The slice() method returns a shallow copy of a portion of an array into a new arrayobject selected from begin to end (end not included). The original array will not be modified.
slice() 方法将数组的一部分的浅拷贝返回到从开始到结束（不包括结束）选择的新数组对象中。不会修改原始数组。
The correct answer:
正确答案：
let arr = [1, 2, 3, 4, 5];
let last = arr.slice(-1)[0];
References: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice
参考资料：https: //developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice
回答by radman
Very late to the party, but for posterity: in ES2015/ES6 you can use Array.prototype.slice. Doesn't mutate the array and a negative number gives you elements from the end of the array as a new array.
聚会很晚，但为了后代：在 ES2015/ES6 中，您可以使用Array.prototype.slice。不改变数组，负数将数组末尾的元素作为新数组。
So to get the last element:
所以要获取最后一个元素：
let arr = [1, 2, 3, 4, 5];
let last = arr.slice(-1); // last = 5
