javascript - typescript 从数组的前端和末尾获取X个元素

Question

我想优化下面的代码，因为它看起来步骤太多。该代码确实有效，但是我想看看是否有更好的方法。我基本上想从 shipmentTracings 数组中获取前 X 个元素和最后 X 个元素。有没有办法优化那部分？

此外，我正在根据 numberOfTracings/2 在数组的左侧和右侧推导我想要的元素。对于奇数，我四舍五入，但你可以看到我正在使用 paddingRight 来使用余数, 如果有的话。还有更好的方法吗？

        const numberOfTracings = environment.shipmentTracingMarkerLimit - this.shipmentTracking.shipmentStops.length;  // i.e. 7
        const paddingLeft = Math.floor(numberOfTracings / 2);
        const paddingRight = numberOfTracings - paddingLeft * 2; //i am doing this because I want to use that extra array spot to be padded.  It 
        const myFirstArr = this.shipmentTracking.shipmentTracings.slice(0, paddingLeft);
        const myFirstArr2 = this.shipmentTracking.shipmentTracings.slice(-(paddingLeft + paddingRight));
        const myFirstArr3 = myFirstArr.concat(myFirstArr2);
        myFirstArr3.forEach((shipmentTracing) => this.createRouteMarkerForTracing(shipmentTracing));

Answer 1

使用评论中的示例，您可以使用 ES2015 spread operator做这样的事情:

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];

const padding = 2;

const firstAndLast = [...fruits.slice(0, padding), ...fruits.slice(-padding)];

console.log(firstAndLast);

编辑:根据padding计算左/右切片的注释更新:

const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango", "Dragon Fruit", "Kiwi", "Apricot", "Lime", "Plantain"];

const getFirstAndLast = (arr, padding) => {
  const left = Math.ceil(padding / 2);
  const right = padding - left;
  return [...arr.slice(0, left), ...arr.slice(-right)];
};

// gets first 4 and last 3 given a padding of 7
const firstAndLast = getFirstAndLast(fruits, 7);

console.log(firstAndLast);