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.
$ npm install on-change
const onChange = require('on-change');
const object = {
foo: false,
a: {
b: [
{
c: false
}
]
}
};
let i = 0;
const watchedObject = onChange(object, function (path, value, previousValue, applyData) {
console.log('Object changed:', ++i);
console.log('this:', this);
console.log('path:', path);
console.log('value:', value);
console.log('previousValue:', previousValue);
console.log('applyData:', applyData);
});
watchedObject.foo = true;
//=> 'Object changed: 1'
//=> 'this: {
// foo: true,
// a: {
// b: [
// {
// c: false
// }
// ]
// }
// }'
//=> 'path: "foo"'
//=> 'value: true'
//=> 'previousValue: false'
//=> 'applyData: undefined'
watchedObject.a.b[0].c = true;
//=> 'Object changed: 2'
//=> 'this: {
// foo: true,
// a: {
// b: [
// {
// c: true
// }
// ]
// }
// }'
//=> 'path: "a.b.0.c"'
//=> 'value: true'
//=> 'previousValue: false'
//=> 'applyData: undefined'
watchedObject.a.b.push(3);
//=> 'Object changed: 3'
//=> 'this: {
// foo: true,
// a: {
// b: [
// {
// c: true
// },
// 3
// ]
// }
// }'
//=> 'path: "a.b"'
//=> 'value: [{c: true}, 3]'
//=> 'previousValue: [{c: true}]'
//=> 'applyData: {
// name: "push",
// args: [3],
// result: 2,
// }'
// Access the original object
onChange.target(watchedObject).foo = false;
// Callback isn't called
// Unsubscribe
onChange.unsubscribe(watchedObject);
watchedObject.foo = 'bar';
// Callback isn't called
Returns a version of object
that is watched. It's the exact same object, just with some Proxy
traps.
Type: object
Object to watch for changes.
Type: Function
Function that gets called anytime the object changes.
The function receives four arguments:
- A path to the value that was changed. A change to
c
in the above example would returna.b.0.c
. - The new value at the path.
- The previous value at the path. Changes in
WeakSets
andWeakMaps
will returnundefined
. - An object with the name of the method that produced the change, the args passed to the method, and the result of the method.
The context (this) is set to the original object passed to onChange
(with Proxy).
Type: object
Options for altering the behavior of onChange.
Type: boolean
Default: false
Deep changes will not trigger the callback. Only changes to the immediate properties of the original object.
Type: Function
Default: Object.is
The function receives two arguments to be compared for equality. Should return true
if the two values are determined to be equal. Useful if you only need a more loose form of equality.
Type: boolean
Default: false
Setting properties as Symbol
won't trigger the callback.
Type: Array<string | symbol>
Default: undefined
Setting properties in this array won't trigger the callback.
Type: boolean
Default: false
Setting properties with an underscore as the first character won't trigger the callback.
Type: boolean
Default: false
The path will be provided as an array of keys instead of a delimited string. Recommended when working with Sets, Maps, or property keys that are Symbols.
Type: boolean
Default: false
Ignore changes to objects that become detached from the watched object.
Type: boolean|string[]
Default: false
Trigger callbacks for each change within specified method calls or all method calls.
Type: Function
The function receives the same arguments and context as the onChange callback. The function is called whenever a change is attempted. Returning true will allow the change to be made and the onChange callback to execute, returning anything else will prevent the change from being made and the onChange callback will not trigger.
Returns the original unwatched object.
Type: object
Object that is already being watched for changes.
Cancels all future callbacks on a watched object and returns the original unwatched object.
Type: object
Object that is already being watched for changes.
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;
- known - Allow only access to known object properties (Uses
Proxy
too) - negative-array - Negative array index support
array[-1]
(UsesProxy
too) - atama - State manager (Uses
Proxy
too) - introspected - Never-ending Proxy with multiple observers (Uses
Proxy
too)