Accumulate Array of Arrays Using forEach

Flatten - Combining Arrays with forEach()

var data = [[1,2,3], [4,5,6], [7,8,9]];
function arrayAdd(aOfAs) {
  var acc = [];
  aOfAs.forEach(function(a) {
    a.forEach(function(el) {
      acc.push(el);
    ;})
  ;});
  return acc;
}
arrayAdd(data);
> [1,2,3,4,5,6,7,8,9]

Same Thing - Flatten with reduce()

var data = [[1,2,3],[4,5,6],[7,8,9]];
var flattenedData = data.reduce(function(acc, value) {
  return acc.concat(value);
}, []);
console.log(flattenedData);
> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Processing every element of an array with reduce()

var data = [1,2,3,4,5];
var doubled = data.reduce(function(acc, value) {
  acc.push(value * 2);
  return acc;
}, []);
console.log(doubled);
> [2, 4, 6, 8, 10]

Selecting some elements of an array with reduce()

var data = [1,2,3,4,5];
var evens = data.reduce(function(acc, value) {
  if (value % 2 === 0) {
    acc.push(value);
  }
  return acc;
}, []);
console.log(evens);
> [2, 4]

Same Thing Using filter()

var evenFiltered = data.filter(function(item) {
  return item % 2 === 0;
});
console.log(evenFiltered);
[2, 4]

Filtered and Mapped

var filteredAndMapped = data.filter(function(value) {
  return value % 2 == 0;
}).map(function(value) {
  return value * 2;
});
console.log(filteredAndMapped);
> [4, 8]