javascript - 使用 findIndex() 从非零元素开始

Question

我想在从零以外的元素开始的数组上使用 findIndex() 。我编写了以下代码，该代码对我有用，但是有更干净的解决方案吗？

let desiredLastElementIndex = refundRequests.map((e,i) =>{
    if(i<numberOfTickets){
        return 0
    }else{
        return Math.round(e.purchasersMinimumPrice - refundRequests[i-1].purchasersMinimumPrice)
        }
        }).findIndex((e, i) => findIndex((e, i) => e !== 0)

例如，当使用indexOf时，我可以传递我想要开始的索引作为第二个参数。

理想情况下，我想做一些类似的事情......

    let desiredLastElementIndex = refundRequests.findIndex((e, i) => {
     e.purchasersMinimumPrice !== refundRequests[i+1].purchasersMinimumPrice
}, INDEXTOSTARTFROM) + 1

Answer 1

您可以定义一个名为 fromIndex() 的辅助方法来包装回调函数，然后再将其传递给 Array.prototype.find()或Array.prototype.findIndex() 。它可以包装回调的其他函数是 Array.prototype.filter() , Array.prototype.forEach() ，和Array.prototype.some() .

function fromIndex(cb, index) {
  return function (e, i, a) {
    return i >= index && cb.call(this, e, i, a);
  };
}

const array = [3, 7, 5, 1, 9];
const f = element => element > 4;

console.log(`value ${array.find(f)} index ${array.findIndex(f)}`);
console.log(`value ${array.find(fromIndex(f, 3))} index ${array.findIndex(fromIndex(f, 3))}`);

在您的示例中，用法如下所示:

let desiredLastElementIndex = refundRequests.findIndex(fromIndex((e, i) => {
  e.purchasersMinimumPrice !== refundRequests[i + 1].purchasersMinimumPrice
}, INDEXTOSTARTFROM)) + 1

<小时/>

为了获得一些额外的乐趣，您可以专门为 find() 和 findIndex() 定义一些 iteratee-last 柯里化(Currying)函数:

const fromIndex = (cb, index = 0) => (e, i, a) => (
  i >= index && cb(e, i, a)
);
const wrap = (impl, apply) => (...args) => (
  f => iteratee => impl(iteratee, f)
)(
  apply(...args)
);

const find = wrap((array, fn) => array.find(fn), fromIndex);
const findIndex = wrap((array, fn) => array.findIndex(fn), fromIndex);

const array = [3, 7, 5, 1, 9];
const f = element => element > 4;

console.log(`value ${find(f)(array)} index ${findIndex(f)(array)}`);
console.log(`value ${find(f, 3)(array)} index ${findIndex(f, 3)(array)}`);

如果/当 F# style pipeline operator一旦符合规范，这将使这些部分功能看起来非常有吸引力:

// find() and findIndex() defined as above
const array = [3, 7, 5, 1, 9];
const f = element => element > 4;

// value 7 index 1
console.log(`value ${array |> find(f)} index ${array |> findIndex(f)}`);
// value 9 index 4
console.log(`value ${array |> find(f, 3)} index ${array |> findIndex(f, 3)}`);