Function reducer

deps/v8/test/mjsunit/object-seal.js:483–483

(accumulator, currentValue)

  assertEquals(arr.flat(), arr);
  assertEquals(arr.join('-'), "a-b-c");
  const reducer = (accumulator, currentValue) => accumulator + currentValue;
  assertEquals(arr.reduce(reducer), "abc");
  assertEquals(arr.reduceRight(reducer), "cba");
  assertEquals(arr.slice(0, 1), ['a']);