What is the `target` in javascript decorators
babeljs, decorator, ecmascript-6, javascript, node.js
Solution
It sounds like you're using the old legacy decorators. Beware that the decorators proposal has moved on since then and the API is still evolving. The proposal is (as I write this) at Stage 2, e.g. "draft" (see this document for details).
The `target` in your `@deprecated` decorator using the old legacy plugin is the object that will ultimately be saved as `Foo.prototype`. Whereas in `@Bar`, it's the `Foo` class constructor itself. That's why in your `@deprecated` decorator, you can't use `new target` (`target` is a non-callable object), but you can use `new target.constructor` (which is `Object`).
But again: This stuff is still in flux.
Problem
I'm playing with javascript decorators but I'm having a hard time with the target which is passed to the decorator function For example, if you have ``` @Bar() class Foo { @deprecated(true) doMagic() {} } function Bar() { return function decorator(target) { } } function deprecated(state) { return function decorator(target, name, config) { return config; } } ``` I would expect that both targets are one and the same thing, right, well it isn't. For example ``` function Bar() { return function decorator(target) { let bar = new target(); // WORKS bar instanceof target; // -> true } } function deprecated(state) { return function decorator(target, name, config) { let bar = new target(); // ERROR let bar = new target.constructor() // WORKS bar instanceof target; // TypeError: Right-hand side of 'instanceof' is not callable bar instanceof target.constructor // WORKS return config; } } ``` As you can see there is a difference between both targets, and my question is what is wrong with that second target I use node v7.8.0 and I'm using the follow babel plugins (.babelrc) ``` { "presets": [ "es2015", "stage-0" ] ``` }