Es6 Map, Foreach, Reduce, and filter details

Suppose we have an array, and each element is a person. There’s a line in front of you

Foreach is when you do something with them, one by one, in any order:

people.forEach(function (dude,index) {
  dude.pickUpSoap();
});Copy the code

A map is when you take a box (a new array) and tell them to drop their wallets in it one by one. You end up with a new array of people’s wallets in the same order as their wallets.

var wallets = people.map(function (dude) {
  return dude.wallet;
});Copy the code

You take your wallet and count it one by one to see how much money is in it? Each time you check one, you add it to the previous sum. So at the end of the day you know how much money everybody has.

var totalMoney = wallets.reduce(function (countedMoney, wallet) {
  returncountedMoney + wallet.money; }, 0); // countedMoney starts receiving 0Copy the code

var fatWallets = wallets.filter(function (wallet) {
  return wallet.money > 100;
});Copy the code

Map and filter are immutable methods, that is, they only return a new array without changing the original array. The filter example is a bit different from the code, but for illustration, So you get the idea.