Javascript过滤器但返回键而不是值

Question

此函数工作正常，但我不希望它返回值，但键：const search = [2342,1900,1800,2310]search = search.filter(function (el) { return el > 2200; });所以它应该返回[0,3]而不是[2342,2310]

Answer 1

您可以获取密钥，然后使用它们访问数组，并基于此进行过滤：

const search = [2342,1900,1800,2310];

const result = Object.keys(search)

  .filter(key => search[key] > 2200)

  .map(key => Number(key))

  

console.dir(result)

或者，对于更有趣的事情：

const search = [2342,1900,1800,2310];

const pipe = (...fns) => x => fns.reduce((v, f) => f(v), x);

const filter = f => a => a.filter(f);

const map = f => a => a.map(f);

const toPairs = o => Object.keys(o)

  .map(k => [k, o[k]]);  

const take = i => a => a[i];

const gte = a => b => b >= a;

const toNumber = x => Number(x);

const bigEnough = gte(2200);

const itemOneIsBigEnough = pipe(

  take(1),

  bigEnough

);

const getTheFirstItemAsANumber = pipe(take(0), toNumber);

const doTheThing = pipe(

  toPairs,

  filter(

    itemOneIsBigEnough

  ),

  map(getTheFirstItemAsANumber),

);

const result = doTheThing(search);

console.dir(result);

Answer 2

您可以获取键并按值检查过滤。

const

    search = [2342, 1900, 1800, 2310],

    indices = [...search.keys()].filter(i => search[i] > 2200);

console.log(indices);

Answer 3

最简单的方法是只是Array#reduce项目：

const search = [2342,1900,1800,2310]

const result = search.reduce(function (result, el, index) {

  if(el > 2200) {

    result.push(index);

  }

  return result;

}, []);

console.log(result);