phaser/v3/src/geom/rectangle/Rectangle.js

//  Encapsulates a 2D rectangle defined by its corner point in the top-left
//  and its extends in x (width) and y (height)

var Rectangle = function (x, y, width, height)
{
    if (x === undefined) { x = 0; }
    if (y === undefined) { y = 0; }
    if (width === undefined) { width = 0; }
    if (height === undefined) { height = 0; }

    this.x = x;

    this.y = y;

    this.width = width;

    this.height = height;
};

Rectangle.prototype.constructor = Rectangle;

Rectangle.prototype = {

    set: function (x, y, width, height)
    {
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;

        return this;
    },

    setPosition: function (x, y)
    {
        if (y === undefined) { y = x; }

        this.x = x;
        this.y = y;

        return this;
    },

    setSize: function (width, height)
    {
        if (height === undefined) { height = width; }

        this.width = width;
        this.height = height;

        return this;
    }

};

Object.defineProperties(Rectangle.prototype, {

    left: {

        enumerable: true,

        get: function ()
        {
            return this.x;
        },

        set: function (value)
        {
            if (value >= this.right)
            {
                this.width = 0;
            }
            else
            {
                this.width = this.right - value;
            }

            this.x = value;
        }

    },

    right: {

        enumerable: true,

        get: function ()
        {
            return this.x + this.width;
        },

        set: function (value)
        {
            if (value <= this.x)
            {
                this.width = 0;
            }
            else
            {
                this.width = value - this.x;
            }
        }

    },

    top: {

        enumerable: true,

        get: function ()
        {
            return this.y;
        },

        set: function (value)
        {
            if (value >= this.bottom)
            {
                this.height = 0;
                this.y = value;
            }
            else
            {
                this.height = (this.bottom - value);
            }
        }

    },

    bottom: {

        enumerable: true,

        get: function ()
        {
            return this.y + this.height;
        },

        set: function (value)
        {
            if (value <= this.y)
            {
                this.height = 0;
            }
            else
            {
                this.height = value - this.y;
            }
        }

    }

});

module.exports = Rectangle;