idempotent-bind

idempotent bind function library.

• Idempotence - Wikipedia, the free encyclopedia

Abstract

A bind function is idempotent if, whenever it is applied twice to any value, it gives the same result as if it were applied once:

bind(bind(x, this), this) === bind(x, this)

ECMAScript' Function.prototype.bind (thisArg [, arg1 [, arg2, …]]) is not idempotent.

x.bind(this).bind(this) !== x.bind(this)

Installation

npm install idempotent-bind

Usage

bind(target, thisArg)

The bind method takes two arguments, target, thisArg, and returns a bound function.

• target: the target function
• thisArg: The value to be passed as the this parameter to the target function when the bound function is called.

import { bind, unbind } from "idempotent-bind"
import {EventEmitter} from "events"
const emitter = new EventEmitter();

class Component {
	componentWillMount(){
		emitter.on("change", bind(this.onChange, this));
	}
	onChange(){
		// do something
	}
	componentWillUnmount(){
		// `unbind` release `bind` from Reference Cache Map and return the bound function.
		emitter.removeListener("change", unbind(this.onChange, this));
		// == emitter.removeListener("change", bind(this.onChange, this));
		// but not release the Reference Cache Map.
	}
}

bind is not support [, arg1 [, arg2, …] like Function.prototype.bind (thisArg [, arg1 [, arg2, …]]).

unbind(target, thisArg)

The unbind method takes two arguments, target, thisArg, and returns a bound function. This unbind behavior is similar to removeChild.

var oldChild = element.removeChild(child) 

two arguments is the same as bind function.

• target: the target function
• thisArg: The value to be passed as the this parameter to the target function when the bound function is called.

import { bind, unbind } from "idempotent-bind"
import assert from "assert"
var f = function () {};
var g = bind(f, this);
assert(g === bind(f, this));
// unbind!!
unbind(f, this);
assert(g !== bind(f, this));

Tests

npm test

Contributing

1. Fork it!
2. Create your feature branch: git checkout -b my-new-feature
3. Commit your changes: git commit -am 'Add some feature'
4. Push to the branch: git push origin my-new-feature
5. Submit a pull request :D

License

MIT