day1.js

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  function part1(arr) {
    return arr.reduce((acc, val) => {
      return acc + val;
    }, 0);
  }

  function part2(arr) {
    let index = 0;
    let freq = 0;
    const history = [];
    while(history.indexOf(freq) === -1) {
      history.push(freq);
      change = arr[index];
      next = freq + change;
      freq = next;
      index = (index + 1) % arr.length;
    }
    return freq;
  }

  testValues = [
    { values: [1, -1], result: 0 },
    { values: [+3, +3, +4, -2, -4], result: 10 },
    { values: [-6, +3, +8, +5, -6], result: 5 },
    { values: [+7, +7, -2, -7, -4], result: 14 }
  ];

  console.log(part1(values));

  testValues.forEach((test, index) => {
    result = part2(test.values);
    console.log(index, result, test.result, result === test.result);
  });
  console.log(part2(values));