1let flattened = [[0, 1], [2, 3], [4, 5]].reduce(
2  function(accumulator, currentValue) {
3    return accumulator.concat(currentValue)
4  },
5  []
6)
7// flattened is [0, 1, 2, 3, 4, 5]
8

1var objs = [
2  {name: "Peter", age: 35},
3  {name: "John", age: 27},
4  {name: "Jake", age: 28}
5];
6
7objs.reduce(function(accumulator, currentValue) {
8  return accumulator + currentValue.age;
9}, 0); // 35 + 27 + 28 = 90

1function getArraySum(a){
2    var total=0;
3    for(var i in a) { 
4        total += a[i];
5    }
6    return total;
7}
8
9var payChecks = [123,155,134, 205, 105]; 
10var weeklyPay= getArraySum(payChecks); //sums up to 722

1var array = [36, 25, 6, 15];
2
3array.reduce(function(accumulator, currentValue) {
4  return accumulator + currentValue;
5}, 0); // 36 + 25 + 6 + 15 = 82

1let nums = [1, 2, 3];
2
3nums.reduce((curr, next) => curr + next);

1// Reduce() method executes a callback function that is passed in
2// on each element of the array, resulting in single output value.
3const array1 = [1, 2, 3, 4];
4const callback = (accumulator, currentValue) => accumulator + currentValue;
5
6// 1 + 2 + 3 + 4
7console.log(array1.reduce(callback));
8// expected output: 10
9
10// 5 + 1 + 2 + 3 + 4
11console.log(array1.reduce(callback, 5));
12// expected output: 15 because the initial value is 5.
13
14// This is how Reduce works.
15// This is a myReduce method which takes a callback and an optional argument 
16// of a default accumulator. If myReduce only receives one argument, then 
17// myReduce will use the first element as the accumulator.
18
19Array.prototype.myReduce = function(callback, acc) {
20    if (!acc) {
21        acc = this.shift();
22    }
23    this.forEach(function(element) {
24        acc = callback(acc, element)
25    })
26    return acc;
27}