Array destructing from Object.entries in Javascript

Question

Here is the code in question:

const posts = [{
  data: {
    id: 1,
    date: "2019-02-03",
    ev_filter_1: ["art", "foodie"],
    ev_filter_2: ["value1", "value2"],
    ev_filter_3: ["value1", "value2"],
    ev_filter_4: ["all", "12+"]
  }
},
  {
    data: {
      id: 2,
      date: "",
      ev_filter_1: ["arti", "foodie"],
      ev_filter_2: ["value1", "value2"],
      ev_filter_3: ["value1", "value2"],
      ev_filter_4: ["all", "19+"]
    }
  },
  {
    data: {
      id: 3,
      date: "2019-02-03",
      ev_filter_1: ["art", "foodie"],
      ev_filter_2: ["value1", "value75"],
      ev_filter_3: ["value1", "value2"],
      ev_filter_4: ["all", "12+"]
    }
  }
];

function sift2(arrObjLit, pattern, ...values) {
  const toMatch = new Set(values)
  const result = arrObjLit.map(o => o.data)
  .filter(o =>
      Object.entries(o)
      .filter(([k, v]) => {
        console.log(`${k}: ${v}`)
        return true
      })
      .filter(([k, v]) => k.startsWith(pattern))
      .filter(([k, v]) => Array.isArray(v))
      .filter(([k, v]) => toMatch.has(v))
          .length > 0
  )
  return result;
}

console.log(...sift2(posts, "ev_", "value75", "12+"));

Which is baffling me. Based on this post I would expect the array destructing in filter to be wrong. And yet, it's not. It's exactly what I am looking for. Why would the destructing be flat in the filter method? Am I observing things wrong?

.filter(o =>
      Object.entries(o)
      .filter(([k, v]) => k.startsWith(pattern))

toMatch.has(v) doesn't work when toMatch is a set of strings and v is an array. — Bergi
– Bergi, Commented Jul 11, 2017 at 6:34

Bergi · Accepted Answer · 2017-07-11 06:37:59Z

3

Because you are now properly nesting the iterations, calling the second filter directly on the output of entries. Notice that you are using

.filter(o => Object.entries(o).filter(…).… )

instead of

.map(Object.entries).filter(o => o.… )

That said, I'd rewrite your function to

function sift2(arrObjLit, pattern, ...values) {
  const toMatch = new Set(values)
  return arrObjLit.filter(o =>
    Object.entries(o.data)
    .some(([k, v]) => {
      console.log(`${k}: ${v}`);
      return k.startsWith(pattern)
          && Array.isArray(v)
          && v.some(x => toMatch.has(x));
    })
  );
}

edited Jul 11, 2017 at 6:37

answered Jul 11, 2017 at 6:32

Bergi

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