class-autobind-decorator

A small, customizable, framework-agnostic, ES5-compatible class-level decorator for automatically binding "class" methods -- i.e., methods on a constructor's prototype object -- to instances, so that this refers to the relevant instance within those methods.

Features:

• Usable with ES6+ React and Preact classes, but also elsewhere (exports a default autoBindMethods decorator, as well as an autoBindMethodsForReact convenience decorator that skips autobinding methods from the React Component Spec that do not require binding)
• Built version is fully ES5-compatible, requiring no ES6+ polyfills
• Supports class methods that have ES6 Symbols as keys
• Accepts configuration options (see examples below), allowing the user to specify the methods that should or should not be bound (supporting both named methods and methods with Symbols as keys in this case, as well), and to specify whether or not to perform certain optimizations
• Does not attempt to redefine methods marked as non-configurable (checks for configurability first!)
• Keeps property descriptors (e.g., writability, enumerability, etc.) consistent between original properties and the corresponding autobound properties
• Does not "magically" autobind properties set on classes/prototypes after the decorator has been applied
• Conforms to the ES6+ "legacy" decorator pattern, and hence is usable as an ES6+ legacy decorator
• Usable as both a "bare," unconfigured decorator (@autoBindMethods) or as a configured decorator (@autoBindMethods(options))
• Documented and tested
• Includes TypeScript declarations for use with TypeScript

Installation

npm install --save class-autobind-decorator

Usage

Note that this is currently only usable as a "class"-level (or, in ES5 terms, a constructor-function-level) decorator. It can't currently be used on individual methods. However, the decorator accepts an options object that can define an array of methods not to bind (using the method names or Symbol keys; see the use of methodsToIgnore in the examples below, as well as the test cases in the tests).

ES6-style as a "legacy" class decorator, without options:

import autoBindMethods from 'class-autobind-decorator';
 
@autoBindMethods // You could also use `@autoBindMethods()` if you want.
class Foo {
    someMethod() {
        return this instanceof Foo;
    }
}
 
const smReference = new Foo().someMethod;
console.log(smReference()); // => `true`

ES6-style as a "legacy" class decorator, with options:

import autoBindMethods from 'class-autobind-decorator';
// NOTE: For React classes, you can use this alternative:
// import { autoBindMethodsForReact } from 'class-autobind-decorator';
 
@autoBindMethods({ methodsToIgnore: ['unboundMethod', 'render'] })
// or:
// @autoBindMethodsForReact({ methodsToIgnore: ['unboundMethod'] })
class MyComponent extends React.Component {
    someComponentMethod() {
        // Do something with `this` here. If the React `onClick`
        // handler below is triggered, `this` will be bound to the
        // component instance.
    }
    
    unboundMethod() {
        // `this` will not be auto-bound in this method, given the
        // options passed in to the decorator.
    }
    
    // This method will not be bound by `autoBindMethods` either (it
    // doesn't need to be).
    render() {
        return (
            <button onClick={this.someComponentMethod} />
        );
    }
}

ES5-style, without options:

var autoBindMethods = require('class-autobind-decorator').default;
 
var Foo = (function () {
    function Foo () {}
    Foo.prototype.someMethod = function () {
        return this instanceof Foo;
    };
    return Foo;
}());
 
autoBindMethods(Foo);
var smReference = new Foo().someMethod;
console.log(smReference()); // => `true`

ES5-style, with options:

var autoBindMethods = require('class-autobind-decorator').default;
var customAutoBinder = autoBindMethods({
    methodsToIgnore: ['secondMethod']
});
 
var Foo = (function () {
    function Foo () {}
    Foo.prototype.firstMethod = function () {
        return this instanceof Foo;
    };
    Foo.prototype.secondMethod = function () {
        return this instanceof Foo;
    };
    return Foo;
}());
 
customAutoBinder(Foo);
var fooInstance = new Foo();
var fmReference = fooInstance.firstMethod;
var smReference = fooInstance.secondMethod;
console.log(fmReference()); // => `true`
console.log(smReference()); // => `false`, due to passed in options

Configuration Options

methodsToIgnore: An array of method names that should not be bound if found on the prototype. See the above examples for usage.

dontOptimize: The default behavior of this decorator is to only bind methods to instances once, and, from that point onward, to store the bound method on the instance itself. You can override this behavior by setting dontOptimize to true. If you do that, the method will be re-bound to the instance on every access; a bound version of the method will not be stored on the instance itself (so, a use case for this might be if you need the instance not to be modified at all).

Building

Clone the repository, run npm install, then, in the main (top-level) repo directory:

npm run build

Compiled code will be placed in the ./build directory. You can also download compiled code directly from this repository.

Running Tests

Clone the repository and go to the main (top-level) repo directory. Be sure to run npm install first, and then:

npm run test

Tests are specified in the ./tests directory, and use mocha and chai. Running the tests also requires a few extra babel dependencies specified in package.json.

Wait... Why did you write yet another auto-bind decorator?

Well, I'm not currently aware of another project that has all of the features mentioned in the "Features" section, above (the ones I am aware of either hard-code React-specific stuff, or don't check whether properties are configurable before trying to redefine them, or inadvertently bind to non-instance objects when methods are accessed first via the prototype, or can't be used as both "bare" (unconfigured) decorators and configured decorators, or don't have TypeScript declarations, and things like that -- no hate, though!). I also just wanted an opportunity to work more directly with decorators, so I used it as a learning experience. :)

License

MIT