minimal janky port of entt to js

tent.js

function ComponentSet() {
  this.entities = [];
  this.indices = []; // could be a hashmap
  this.components = [];
  this.size = 0;
}

ComponentSet.prototype.insert = function (entity, component) {
  this.entities.push(entity);
  this.components.push(component);
  this.indices[entity] = this.size;
  this.size++;
};

ComponentSet.prototype.replace = function (entity, component) {
  this.components[this.indices[entity]] = component;
};

ComponentSet.prototype.assign = function (entity, component) {
  if(this.contains(entity))
    this.replace(entity, component);
  else
    this.insert(entity, component);
}

ComponentSet.prototype.remove = function (entity) {
  if(!this.contains(entity)) return;
  let last = this.entities[this.size-1];
  this.entities[this.indices[entity]] = last;
  this.indices[last] = this.indices[entity];
  this.size--;
};

ComponentSet.prototype.get = function (entity) {
  return this.components[this.indices[entity]];
};

ComponentSet.prototype.contains = function (entity) {
  return this.entities[this.indices[entity]] == entity;
};

ComponentSet.prototype.eachEntity = function (f) {
  for (var i = this.size-1; i >= 0; i--) {
    f(this.entities[i]);
  }
}

ComponentSet.prototype.eachComponent = function (f) {
  for (var i = this.size-1; i >= 0; i--) {
    f(this.components[i]);
  }
}

ComponentSet.prototype.each = function (f) {
  for (var i = this.size-1; i >= 0; i--) {
    f(this.entities[i], this.components[i]);
  }
}

/*****************************/

function View(componentSets) {
  this.componentSets = componentSets == undefined ? [] : componentSets;
}

View.prototype.each = function (f) {
  if(this.componentSets.length == 0) return;
  if(this.componentSets.length == 1) return this.componentSets[0].each(f);

  let smallestSet = this.componentSets[0];
  for (var i = this.componentSets.length-1; i >= 0; i--)
    if(this.componentSets[i].size < smallestSet)
      smallestSet = this.componentSets[i];
  var componentCount = this.componentSets.length;
  var arguments = new Array(componentCount+1);
  for (var i = smallestSet.size-1; i >= 0; i--) {
    let e = smallestSet.entities[i];
    arguments[0] = e;
    var j=0;
    for (; j < componentCount; j++) {
      if(!this.componentSets[j].contains(e))
        break;
      arguments[j+1] = this.componentSets[j].get(e);
    }
    if(j < componentCount) continue;
    f.apply(null, arguments)
  }
};

let positions = new ComponentSet();
let names = new ComponentSet();

positions.assign(7, {x:90, y:12})
positions.assign(3, {x:90, y:12})
positions.assign(9, {x:90, y:12})
positions.assign(9, {x:1, y:3})
names.assign(3, "ramsey")
names.assign(9, "jim")
names.assign(8, "absent")
positions.remove(3);

var v = new View([positions, names])

let i = 4;
// names.each((e, c) => console.log(e, c))
v.each((e, n, c) => console.log("view", e, n, c))

// console.log(names)