/code/javascript/boundarray.js

// creates a proxied array, optionally initialized,
// with optional getter and validate/changed hooks
function proxied_array (spec) {
	var proxy = new Proxy(spec.init || [], {
		get: function (obj, prop) {
			// call proxy when defined
			if (spec.get) spec.get.call(obj, prop);
			// return appropriately bound proxy functions
			if (prop in obj && Function.bind === obj[prop].bind) {
				if (spec.changed)
					return function bound () {
						var tmp = this.slice();
						var ret = this[prop].apply(tmp, arguments);
						console.log(JSON.stringify({
							"event": "method called",
							"this": this,
							"tmp": tmp,
							"method": prop,
							"arguments": arguments,
							"returning": ret
						}));
						if (this != tmp && tmp.forEach(spec.validate)) {
							this[prop].apply(this, arguments);
							if (spec.changed) spec.changed.call(this);
						}
						return ret;
					}.bind(obj);
				return obj[prop].bind(obj);
			}
			// and pass through read requests invisibly
			return obj[prop];
		},
		set: function (array, index, value) {
			// call proxy if defined
			console.log(JSON.stringify({
				"event": "value set",
				"array": array,
				"index": index,
				"value": value
			}));
			if (spec.validate && spec.validate(value, index, array)) {
				array[index] = value;
				if (spec.changed) spec.changed.call(array);
			}
			return value;
		}
	});
	return proxy;
}
// creates an permanent fixed-length proxied array as a named propery
function bind_array (host, property, spec) {
	Object.defineProperty(host, property, (function (spec) {
		var proxied = new proxied_array(spec);
		return {
			get: function () { return proxied; },
			set: function (d) {
				console.log(JSON.stringify({
					"event": "array set",
					"data": d
				}));
				if (!Array.isArray(d))
					throw new TypeError("cannot change data type");
				if (d.length != proxied.length)
					throw new TypeError("array is of the wrong length");
				if (d.forEach(spec.validate)) {
					spec.init = d;
					proxied = new proxied_array(spec);
					if (spec.changed) spec.changed.call(proxied);
				}
			}
		};
	})(spec));
}
// example for testing and learning
bind_array(window, "foo", {
	init: [0, 0, 0],
	validate: function (value, index, array) {
		console.log(JSON.stringify({
			"event": "validate",
			"value": value,
			"index": index,
			"array": array
		}));
		if (isNaN(value - 0))
			throw new TypeError("this array only holds numbers");
		if ("length" === index)
			throw new TypeError("cannot redefine array length");
		if (array.length <= index - 0)
			throw new RangeError("specified index is out of range");
		return true;
	},
	changed: function () {
		console.log(JSON.stringify({
			"event": "changed",
			"this": this
		}));
	}
});
// */
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