gawk

gawk

Gawk wraps JavaScript objects and arrays using ES2015 proxies making them observable. Once a JavaScript object (or array) is gawked, you can listen for changes including deeply nested changes.

Only objects and arrays can be gawked. All other types are passed through.

Gawked objects and arrays can be interacted with as if they were regular objects/arrays. Built-in functions such as JSON.stringify() work as expected.

Note: gawk uses ES2015 proxies and thus requires Node.js 6 or newer.

Installation

npm i --save gawk

Examples

import gawk from 'gawk';

const obj = gawk({
    foo: 'bar'
});

gawk.watch(obj, (obj, src) => {
    console.info('object changed!');
    console.info('new value =', obj);
});

obj.foo = 'baz';

console.info(obj); // { foo: 'baz' }

You can also be notified if a deep child is changed:

const obj = gawk({
    foo: {
        bar: ['a', 'b']
    }
});

gawk.watch(obj, (obj, src) => {
    console.info('object changed!');
    console.info('new value =', obj);
});

obj.foo.bar.push('c', 'd');

console.info(obj); // { foo: { bar: ['a', 'b', 'c', 'd'] } }

To filter watch notifications, simply pass in the property name or array of property names used to filter the gawk object.

const obj = gawk({
	foo: {
		bar: 'hello'
	}
});

gawk.watch(obj, [ 'foo', 'bar' ], value => {
	console.info(`bar changed to ${value}`);
});

obj.foo.bar = 'world!';

To stop watching, simply call gawk.unwatch() with the original listener function.

const obj = gawk({ /* ... */ });

function onChange(obj, src) {
	console.log('changed!');
}

gawk.watch(obj, onChange);

obj.foo = 'bar';

gawk.unwatch(obj, onChange);

obj.foo = 'baz'; // does not fire onChange()

To update an object and preserve the listeners, you can use the gawk.set() function.

const obj = gawk({
	foo: 'bar'
});

gawk.watch(obj, () => {
	console.log('changed!');
});

gawk.set(obj, { baz: 'wiz' });

console.log(obj); // { baz: 'wiz' }

obj.baz = 'wow';

console.log(obj); // { baz: 'wow' }

API

gawk(obj)

Gawks the specified object.

• obj - (Object) The object to gawk.

If obj is not an object, is null, or is a built-in object such as JSON or Math, then the original value is returned, otherwise it returns the gawked object.

Note that the returned object is a proxy-wrapped version of the original input object. You can interact with the object as you normally would. Some Array methods are wrapped to suppress multiple change notifications for a single call or to workaround limitations of the proxied objects.

isGawked(obj)

Determines if an variable is a gawked object.

• obj - (Object) The object to check if gawked.

Returns true if the specified object has been gawked, otherwise false

gawk.set(dest, src)

gawk.set(dest, src, compareFn)

Replaces the entire definition of a gawked object with another object or array while preserving any listeners and dispatches change nofications afterwards.

• dest - (Object|Array) The destination object. It will be automatically gawked if not already.
• src - (Object|Array) The source object or array to copy from.
• compareFn - (Function) An optional function to call when comparing elements of an array.

Returns the original dest object.

gawk.watch(subject, listener)

gawk.watch(subject, filter, listener)

Starts watching the specified gawked object for changes.

• subject - (Object) The gawked object to watch.
• filter - (Array[String] | String) [optional] A list of one or more nested namespaces to filter. When a filter is not specified, then it watches the entire object for changes.
• listener - (Function) The function to call when a change occurs.

Returns the original subject value.

The filter is works by matching only a specific namespace pattern. For example, say you have a gawked object { foo: { bar: { baz: 'wiz' } } } and filtering by [ 'foo', 'bar' ]. When you set foo.bar.baz = 'pow', the listener function will be called with the value { baz: 'pow' }. When you set foo.bar.raf = 'muk', this change will not be emitted.

gawk.unwatch(obj)

gawk.unwatch(obj, fn)

Stops watching a gawked object.

• subject - (Object) The gawked object to watch.
• listener - (Function) [optional] The function to call when a change occurs. When a listener is not specified, all listeners are removed from the gawked object.

Returns the original subject value.

gawk.merge(obj, ...objs)

Performs a shallow merge of one or more objects into the specified gawked object.

• obj - (Object) The gawked object to merge values into.
• ...objs - (Object) One or more objects to merge in.

Returns the original gawked object obj.

Note that subsequent object properties will overwrite existing values. Only a single change event is emitted after all objects have been merged.

gawk.mergeDeep(obj, ...objs)

Performs a deep merge of one or more objects into the specified gawked object.

• obj - (Object) The gawked object to merge values into.
• ...objs - (Object) One or more objects to merge in.

Returns the original gawked object obj.

Just as gawk.merge(), subsequent object properties will overwrite existing values. Only a single change event is emitted after all objects have been merged.

If the destination is an array, the two arrays are concatenated.

Performance

Each gawked object is wrapped in a Proxy and contains a object with the gawked object state: listeners, parents, previous values, and notification queue. These data structures are created on an as needed basis. A gawked object with no listeners uses an insignificant amount of memory. However, if you have an object with many levels of deeply nested objects, it could add up quickly.

As soon as listeners are added via gawk.watch(), it will create the Map of listeners. If you add a filter, then a WeakMap of previous values gets created. Each gawked object also tracks its parents using a Set. Again, if filters are not used or the object is not nested (i.e. has no parent), then there's not a significant amount of memory used.

For runtime performance, the more listeners, the slower the notification system is. This is especially true if the object being modified is deeply nested. Notifications are propagated through each parent and each parent's parent and so on.

There aren't any official benchmarks. It's up to you to decide if Gawk is right for your app. Exercise common sense. Don't gawk objects with several dozens of deeply nested objects. Don't add thousands of listeners.

Upgrading to v4

Gawk v4 has dropped all gawk data types. You must always call gawk().

Change all new GawkObject() calls to gawk({}) and new GawkArray() to gawk([]).

Since Gawk v3 and newer uses ES6 Proxies, you no longer need to call obj.get(), obj.set(), obj.delete(), etc.

Methods obj.watch(), obj.merge(), and obj.mergeDeep() have moved to gawk.watch(), gawk.merge(), and gawk.mergeDeep(). The first argument must be a gawk object.

Starting in v3, Gawk no longer hashes values. This means speed. Gawk v3+ is about 19 times faster than v1 and v2.

License

MIT