23

I'm using babelify version 6.3.0 set to stage 0. ES6 / ES7 are working great. However when I try to use JavaScript's proxy functionality:

set product(product={}) {
  this._product = new Proxy({}, {})
}

I get:

ReferenceError: Can't find variable: Proxy

Any ideas?

1

3 Answers 3

35

From the Babel website:

Due to the limitations of ES5, Proxies cannot be transpiled or polyfilled. See support in various JavaScript engines.

Sign up to request clarification or add additional context in comments.

4 Comments

Well, that's unfortunate. The Chrome team released a polyfill: github.com/GoogleChrome/proxy-polyfill, in case that helps anyone.
Apparently is is doable in ES5, according to this package: npmjs.com/package/babel-plugin-proxy
@trusktr Technically speaking, yes but as the creators said "[i]t is not suitable for production environments because performance impact is huge." They replace every single property access with a call to a special function.
@BryceJohnson That polyfill does not allow dynamic keys. It seals your object.
5

You cannot proxy a full object with all the traps but you can create proxied properties for get and set at least.

var proxy = {}

Object.defineProperty(proxy, 'a', {
  get: function() { return bValue; },
  set: function(newValue) { bValue = newValue; }
});

You can even wrap it around a method

function proxyVar(obj, key, initVal) {
  Object.defineProperty(obj, key, {
    get: function() { return bValue*2; },
    set: function(newValue) { bValue = newValue; }
    value: initVal
  });
}

And then:

var proxy = {}

proxyVar(proxy, 'a', 10)

console.log(proxy.a) // prints 20
proxy.a = 20
console.log(proxy.a) // prints 40

Comments

2

Babel translates ES6/ES7 code (assuming you've connected the appropriate presets) into valid ES5 code.

I'm afraid that there's no way to express ES6 proxies via ES5 syntax.

You can see that proxies don't nave any equivalent on es6-features site. There's also a warning about it in the bottom of 'proxies' section of Babel docs.

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.