Checks if an element is inside another or if it collides with another. - http://stackoverflow.com/a/19614185/1250044

README.md

Usage:

var player = new Rect(0, 0, 100, 100);
var target = new Rect(50, 50, 100, 100);
player.is = new AABB(player);

player.is.inside(target);
player.is.colliding(target);
player.is.containing(target);

Union & Intersect from https://github.com/johnhornsby/geom/blob/44f9989bb964e51ce3e5f55027b415c28f3edffd/src/rectangle.js

aabb.js

var Rect = function (top, left, width, height) {
  this.top = top || 0;
  this.left = left || 0;
  this.width = width || 0;
  this.height = height || 0;
  this.right = this.left + this.width;
  this.bottom = this.top + this.height;
};

Rect.prototype = {
  set: function (top, left, width, height) {
    this.top = top || this.top;
    this.left = left || this.left;
    this.width = width || this.width;
    this.height = height || this.height;
    this.right = this.left + this.width;
    this.bottom = this.top + this.height;
  },

  union: function(toUnion) {
    var union = new Rect();
    union.left = Math.min(this.left, toUnion.left);
    union.top = Math.min(this.top, toUnion.top);
    union.width = Math.max(this.left + this.width, toUnion.left + toUnion.width) - union.left;
    union.height = Math.max(this.top + this.height, toUnion.top + toUnion.height) - union.top;
    return union;
  },

  intersect: function(rect) {
    var rectI = new Rect()
    rectI.left = Math.max(this.left, rect.left)
    rectI.top = Math.max(this.top, rect.top)
    rectI.right = Math.min(this.right, rect.right)
    rectI.bottom = Math.min(this.bottom, rect.bottom)
    return rectI
  }
}



var AABB = function (rect) {
  this.top = rect.top;
  this.left = rect.left;
  this.width = rect.width;
  this.height = rect.height;
  this.right = rect.right;
  this.bottom = rect.bottom;
};

AABB.prototype = {
  colliding: function (other) {
    return !(
      this.top > other.bottom ||
      this.right < other.left ||
      this.bottom < other.top ||
      this.left > other.right
    );
  },

  containing: function (other) {
    return (
      this.left <= other.left &&
      other.left < this.width &&
      this.top <= other.top &&
      other.top < this.height
    );
  },

  inside: function (other) {
    return (
      ((other.top <= this.top) && (this.top <= other.bottom)) &&
      ((other.top <= this.bottom) && (this.bottom <= other.bottom)) &&
      ((other.left <= this.left) && (this.left <= other.right)) &&
      ((other.left <= this.right) && (this.right <= other.right))
    );
  }
};

thats pretty awesome, nicely done.

@lgubenis Thanks for the laudatory words :)