phaser/src/utils/Class.js

/**
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2020 Photon Storm Ltd.
 * @license      {@link https://opensource.org/licenses/MIT|MIT License}
 */

//  Taken from klasse by mattdesl https://github.com/mattdesl/klasse

function hasGetterOrSetter (def)
{
    return (!!def.get && typeof def.get === 'function') || (!!def.set && typeof def.set === 'function');
}

function getProperty (definition, k, isClassDescriptor)
{
    //  This may be a lightweight object, OR it might be a property that was defined previously.

    //  For simple class descriptors we can just assume its NOT previously defined.
    var def = (isClassDescriptor) ? definition[k] : Object.getOwnPropertyDescriptor(definition, k);

    if (!isClassDescriptor && def.value && typeof def.value === 'object')
    {
        def = def.value;
    }

    //  This might be a regular property, or it may be a getter/setter the user defined in a class.
    if (def && hasGetterOrSetter(def))
    {
        if (typeof def.enumerable === 'undefined')
        {
            def.enumerable = true;
        }

        if (typeof def.configurable === 'undefined')
        {
            def.configurable = true;
        }

        return def;
    }
    else
    {
        return false;
    }
}

function hasNonConfigurable (obj, k)
{
    var prop = Object.getOwnPropertyDescriptor(obj, k);

    if (!prop)
    {
        return false;
    }

    if (prop.value && typeof prop.value === 'object')
    {
        prop = prop.value;
    }

    if (prop.configurable === false)
    {
        return true;
    }

    return false;
}

/**
 * Extends the given `myClass` object's prototype with the properties of `definition`.
 *
 * @function extend
 * @param {Object} ctor The constructor object to mix into.
 * @param {Object} definition A dictionary of functions for the class.
 * @param {boolean} isClassDescriptor Is the definition a class descriptor?
 * @param {Object} [extend] The parent constructor object.
 */
function extend (ctor, definition, isClassDescriptor, extend)
{
    for (var k in definition)
    {
        if (!definition.hasOwnProperty(k))
        {
            continue;
        }

        var def = getProperty(definition, k, isClassDescriptor);

        if (def !== false)
        {
            //  If Extends is used, we will check its prototype to see if the final variable exists.

            var parent = extend || ctor;

            if (hasNonConfigurable(parent.prototype, k))
            {
                //  Just skip the final property
                if (Class.ignoreFinals)
                {
                    continue;
                }

                //  We cannot re-define a property that is configurable=false.
                //  So we will consider them final and throw an error. This is by
                //  default so it is clear to the developer what is happening.
                //  You can set ignoreFinals to true if you need to extend a class
                //  which has configurable=false; it will simply not re-define final properties.
                throw new Error('cannot override final property \'' + k + '\', set Class.ignoreFinals = true to skip');
            }

            Object.defineProperty(ctor.prototype, k, def);
        }
        else
        {
            ctor.prototype[k] = definition[k];
        }
    }
}

/**
 * Applies the given `mixins` to the prototype of `myClass`.
 *
 * @function mixin
 * @param {Object} myClass The constructor object to mix into.
 * @param {Object|Array<Object>} mixins The mixins to apply to the constructor.
 */
function mixin (myClass, mixins)
{
    if (!mixins)
    {
        return;
    }

    if (!Array.isArray(mixins))
    {
        mixins = [ mixins ];
    }

    for (var i = 0; i < mixins.length; i++)
    {
        extend(myClass, mixins[i].prototype || mixins[i]);
    }
}

/**
 * Creates a new class with the given descriptor.
 * The constructor, defined by the name `initialize`,
 * is an optional function. If unspecified, an anonymous
 * function will be used which calls the parent class (if
 * one exists).
 *
 * You can also use `Extends` and `Mixins` to provide subclassing
 * and inheritance.
 *
 * @class Phaser.Class
 * @constructor
 * @param {Object} definition a dictionary of functions for the class
 * @example
 *
 *      var MyClass = new Phaser.Class({
 *
 *          initialize: function() {
 *              this.foo = 2.0;
 *          },
 *
 *          bar: function() {
 *              return this.foo + 5;
 *          }
 *      });
 */
function Class (definition)
{
    if (!definition)
    {
        definition = {};
    }

    //  The variable name here dictates what we see in Chrome debugger
    var initialize;
    var Extends;

    if (definition.initialize)
    {
        if (typeof definition.initialize !== 'function')
        {
            throw new Error('initialize must be a function');
        }

        initialize = definition.initialize;

        //  Usually we should avoid 'delete' in V8 at all costs.
        //  However, its unlikely to make any performance difference
        //  here since we only call this on class creation (i.e. not object creation).
        delete definition.initialize;
    }
    else if (definition.Extends)
    {
        var base = definition.Extends;

        initialize = function ()
        {
            base.apply(this, arguments);
        };
    }
    else
    {
        initialize = function () {};
    }

    if (definition.Extends)
    {
        initialize.prototype = Object.create(definition.Extends.prototype);
        initialize.prototype.constructor = initialize;

        //  For getOwnPropertyDescriptor to work, we need to act directly on the Extends (or Mixin)

        Extends = definition.Extends;

        delete definition.Extends;
    }
    else
    {
        initialize.prototype.constructor = initialize;
    }

    //  Grab the mixins, if they are specified...
    var mixins = null;

    if (definition.Mixins)
    {
        mixins = definition.Mixins;
        delete definition.Mixins;
    }

    //  First, mixin if we can.
    mixin(initialize, mixins);

    //  Now we grab the actual definition which defines the overrides.
    extend(initialize, definition, true, Extends);

    return initialize;
}

Class.extend = extend;
Class.mixin = mixin;
Class.ignoreFinals = false;

module.exports = Class;