Javascript嵌套与ES6循环

Question

I guys, I have a nested for loop but I want to do it with an Array map/ES6 way but how does that work with nested forloops?

        for (var i = 0; i < enemy.ships.length; i++) {
        for (var n = 0; n < enemy.ships[i].location.length; n++) {
            if (obj.coordination == enemy.ships[i].location[n]) hit = true;
        }
    };

I know how to do it when it as not a forloop

players.map(function(player){if(player.id != socket.id) return enemy = player});

But I can't seem to understand how it should be with Array Maps or something else.

I need to match the location of the ships location & obj.coordination. This is the enemy.ships variable I need to check

    [ { type: 'Aircaft',
    size: 5,
    rekt: false,
    available: 1,
    location: [] },
  { type: 'Battleship',
    size: 4,
    rekt: false,
    available: 1,
    location: [ 77, 76, 75, 74 ] },
  { type: 'Destroyer',
    size: 3,
    rekt: false,
    available: 2,
    location: [ 54, 44, 34 ] },
  { type: 'Submarine',
    size: 3,
    rekt: false,
    available: 3,
    location: [] },
  { type: 'Patrolboat',
    size: 2,
    rekt: false,
    available: 4,
    location: [] } ]

Answer 1

If all you are looking for is whether any location on any ship matches (and not returning the ship that was hit, et cetera), you can use something like:

const hit = enemy.ships
  .map(ship => ship.location)
  .some(coordinates => coordinates.some(coordinate => coordinate === obj.coordination ));

If you wanted to return the ship that was hit (or the ships, if multiple ships were allowed to share the same coordinates):

const hitShips = enemy.ships
  .filter(ship => ship.location.some( coordinate => coordinate === obj.coordination ));

Your example of map is also a little... off.

The goal of map isn't to cause side-effects (in fact, it's specifically meant to avoid all side-effects).
The goal of map is to take one array of objects and return a brand new array of the exact same length, where you have filled the new array based on the objects of the old array.

[1, 2, 3].map( x => x + 1 ); // [2, 3, 4]
["a", "b", "c"].map( x => x.toUpperCase() ); // ["A", "B", "C"]

If you just want to check each item and cause side-effects (change a value that exists outside of the function passed in) then use forEach .

Answer 2

You could use the forEach method to do it in a more functional way. However you won't be able to break from it once the location matches. Additional ref: how to stop Javascript forEach?

enemy.ships.forEach((ship) => {
    ship.location.forEach((location) => {
        if (obj.coordination === location)
            hit = true;
    })
})

Answer 3

You could use Array.prototype.find and filter:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

For example:

var compareLocation = (a, b) => a.length === b.length && a.filter((v, i) => v === b[i]).length === a.length;
var enemyShipFound = enemy.ships.find(ship => compareLocation(obj.coordination, ship.location));