JavaScript array flatten

array_flatten.js

const { deepStrictEqual } = require("assert");

function flat(data) {
  function* _flat(arr) {
    for (const v of arr) {
      if (v instanceof Array) {
        yield* _flat(v);
      } else {
        yield v;
      }
    }
  }
  return [..._flat(data)];
}

const testData = [
  {
    name: "1",
    param: [],
    want: []
  },
  {
    name: "",
    param: [1, ["a", [1, 2, [3, 4]]]],
    want: [1, "a", 1, 2, 3, 4]
  },
  {
    name: "2",
    param: [1, 2, 3, 4],
    want: [1, 2, 3, 4]
  }
];

for (const { name, param, want } of testData) {
  deepStrictEqual(flat(param), want, `${name} tests failed`);
}