on-change

Watch an object or array for changes

It works recursively, so it will even detect if you modify a deep property like obj.a.b[0].c = true.

Uses the Proxy API.

Install

$ npm install on-change

Usage

const onChange = require('on-change');

const object = {
	foo: false,
	a: {
		b: [
			{
				c: false
			}
		]
	}
};

let i = 0;
const watchedObject = onChange(object, () => {
	console.log('Object changed:', ++i);
});

watchedObject.foo = true;
//=> 'Object changed: 1'

watchedObject.a.b[0].c = true;
//=> 'Object changed: 2'

API

onChange(object, onChange)

Returns a version of object that is watched. It's the exact same object, just with some Proxy traps.

object

Type: Object

Object to watch for changes.

onChange

Type: Function

Function that gets called anytime the object changes.

Use-case

I had some code that was like:

const foo = {
	a: 0,
	b: 0
};

// …

foo.a = 3;
save(foo);

// …

foo.b = 7;
save(foo);


// …

foo.a = 10;
save(foo);

Now it can be simplified to:

const foo = onChange({
	a: 0,
	b: 0
}, () => save(foo));

// …

foo.a = 3;

// …

foo.b = 7;

// …

foo.a = 10;

Related

• known - Allow only access to known object properties (Uses Proxy too)
• negative-array - Negative array index support array[-1] (Uses Proxy too)

License

MIT © Sindre Sorhus