( function( global ) {
	function number( v ) {
		return v === undefined ? 0 : Number( v );
	}

	function different( u, v ) {
		return u !== v && ! ( isNaN( u ) && isNaN( v ) );
	}

	function DOMRect( xArg, yArg, wArg, hArg ) {
		let x, y, width, height, left, right, top, bottom;

		x = number( xArg );
		y = number( yArg );
		width = number( wArg );
		height = number( hArg );

		Object.defineProperties( this, {
			x: {
				get: function() {
					return x;
				},
				set: function( newX ) {
					if ( different( x, newX ) ) {
						x = newX;
						left = right = undefined;
					}
				},
				enumerable: true,
			},
			y: {
				get: function() {
					return y;
				},
				set: function( newY ) {
					if ( different( y, newY ) ) {
						y = newY;
						top = bottom = undefined;
					}
				},
				enumerable: true,
			},
			width: {
				get: function() {
					return width;
				},
				set: function( newWidth ) {
					if ( different( width, newWidth ) ) {
						width = newWidth;
						left = right = undefined;
					}
				},
				enumerable: true,
			},
			height: {
				get: function() {
					return height;
				},
				set: function( newHeight ) {
					if ( different( height, newHeight ) ) {
						height = newHeight;
						top = bottom = undefined;
					}
				},
				enumerable: true,
			},
			left: {
				get: function() {
					if ( left === undefined ) {
						left = x + Math.min( 0, width );
					}
					return left;
				},
				enumerable: true,
			},
			right: {
				get: function() {
					if ( right === undefined ) {
						right = x + Math.max( 0, width );
					}
					return right;
				},
				enumerable: true,
			},
			top: {
				get: function() {
					if ( top === undefined ) {
						top = y + Math.min( 0, height );
					}
					return top;
				},
				enumerable: true,
			},
			bottom: {
				get: function() {
					if ( bottom === undefined ) {
						bottom = y + Math.max( 0, height );
					}
					return bottom;
				},
				enumerable: true,
			},
		} );
	}

	global.DOMRect = DOMRect;
}(
	// Support `module.exports` to facilitate unit test.
	typeof module === 'undefined' ? this : module.exports
) );