JavaScript：函数返回最接近的值

Question

I am trying to return the value of the closest object to my position in a function.

I tried to put the entities in a array and than I tried return closest object to my position with a for loop, but it did not work. How can I do this?

function getMyEntity() {
  return Game.currentGame.world.localPlayer.entity.getFromTick();
}

function getOtherEntity() {
  var MyPlayerEntity = getMyEntity();

  var entities = Game.currentGame.world.entities;
  for (var uid in entities) {
    // how i get closest entity to my player entity here?
    var gameObject = entities[uid].fromTick;

    console.log(entities[uid].fromTick.position, MyPlayerEntity.position)
    if (gameObject.entityClass == "Prop" && gameObject.uid !== MyPlayerEntity.uid) {
      return gameObject;
    }
  }
}

function aimAssist() {
  var MyPlayerEntity = getMyEntity();
  var OtherEntity = getOtherEntity();
  if (OtherEntity == undefined) return

  var aimPosition = {
    x: OtherEntity.position.x - MyPlayerEntity.position.x,
    y: OtherEntity.position.y - MyPlayerEntity.position.y
  }
  return aimPosition;
}

Answer 1

I'll give you a bad advice, for now it'll work, as your game grows it will be bad because of O(n^2) complexity. Read a bit about quadtrees and see if you can do that. Meanwhile you can compare the euclidean distance, do not need to take the square root:

Object.keys(entities)
.map(function(d,i){
  var dx = entities[d].fromTick.position.x - MyPlayerEntity.position.x, 
       dy = entities[d].fromTick.position.y - MyPlayerEntity.position.y,
       result = {D:(dx * dx) + (dy + dy), obj:entities[d] , valueOf: function(){return this.D};
  return result;
}).sort(function(a,b){
    return a-b;
})[0].obj; //this returns the closest one

So your original function becomes this:

function getOtherEntity() {
  var MyPlayerEntity = getMyEntity();

  var entities = Game.currentGame.world.entities;
  return Object.keys(entities)
    .map(function(d,i){
      var dx = entities[d].fromTick.position.x - MyPlayerEntity.position.x, 
           dy = entities[d].fromTick.position.y - MyPlayerEntity.position.y,
           result = {D:(dx * dx) + (dy + dy), obj:entities[d] , valueOf: function(){return this.D};
      return result;
    }).sort(function(a,b){
        return a-b;
    })[0].obj; //this returns the closest one
}

Answer 2

I'd create an array of objects which contain the Object-ID and distance, and sort it by distance. The first array-item is the closest to the player.

The array may look like [{uid: 1234, distance: 12}, {uid: 1235, distance: 16}, ...]

You can sort arrays with arrayName.sort(sortingFunction)

Answer 3

assuming you can get x and y coordinates from gameObject.position and MyPlayerEntity.position you could use a bit of Pitagoras: c^2 = a^2 +b^2, with c being the distance

let a = gameObject.position.x - MyPlayerEntity.position.x;
let b = gameObject.position.y - MyPlayerEntity.position.y;
let distanceSquared = a*a + b*b;

Since you don't seem to need the exact distance and sqrt() is expensive, you can use the value in distanceSquared and other variables declared outside of the loop to keep track

let closestDistance;
let closest;

to make the proper comparisons

if(distanceSquared < closestDistance){
    closestDistance = distanceSquared;
    closest = gameObject;
}

After you loop through the array, the closest entity reference should be:

return closest;