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))

Answer 1

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));
    })
  );
}