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
import onChange from 'on-change';
const object = {
foo: false,
a: {
b: [
{
c: false
}
]
}
};
let index = 0;
const watchedObject = onChange(object, function (path, value, previousValue, applyData) {
console.log('Object changed:', ++index);
console.log('this:', this);
console.log('path:', path);
console.log('value:', value);
console.log('previousValue:', previousValue);
console.log('applyData:', applyData);
});
watchedObject.foo = true;
watchedObject.a.b[0].c = true;
watchedObject.a.b.push(3);
onChange.target(watchedObject).foo = false;
onChange.unsubscribe(watchedObject);
watchedObject.foo = 'bar';
API
onChange(object, onChange, options?)
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.
The function receives four arguments:
- A path to the value that was changed. A change to
c in the above example would return a.b.0.c.
- The new value at the path.
- The previous value at the path. Changes in
WeakSets and WeakMaps will return undefined.
- 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).
options
Type: object
Options for altering the behavior of onChange.
isShallow
Type: boolean
Default: false
Deep changes will not trigger the callback. Only changes to the immediate properties of the original object.
equals
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.
ignoreSymbols
Type: boolean
Default: false
Setting properties as Symbol won’t trigger the callback.
ignoreKeys
Type: Array<string | symbol>
Default: undefined
Setting properties in this array won’t trigger the callback.
ignoreUnderscores
Type: boolean
Default: false
Setting properties with an underscore as the first character won’t trigger the callback.
pathAsArray
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.
ignoreDetached
Type: boolean
Default: false
Ignore changes to objects that become detached from the watched object.
details
Type: boolean|string[]
Default: false
Trigger callbacks for each change within specified method calls or all method calls.
When enabled, mutating array and collection methods will emit per-item paths (for example selectedFeatures.0) instead of the collection path. Use details: ['forEach'] to expand only specific methods.
onValidate
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.
onChange.target(object)
Returns the original unwatched object.
object
Type: object
Object that is already being watched for changes.
onChange.unsubscribe(object)
Cancels all future callbacks on a watched object and returns the original unwatched object.
object
Type: object
Object that is already being watched for 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;
- known - Allow only access to known object properties (Uses
Proxy too)
- negative-array - Negative array index support
array[-1] (Uses Proxy too)
- atama - State manager (Uses
Proxy too)
- introspected - Never-ending Proxy with multiple observers (Uses
Proxy too)
Maintainers
评论