How do I assign a value using = when a setter is passed?

Question

I am write a compatibility layer over a legacy library function whose internal signature looks like —

function legacyLibraryFunction(context) {
  context.foo.bar = "data"
  return context
}

The new system however, doesn't recommend assigning custom properties directly to context and instead recommends using the context.set() method.

How do I pass context from the new system to the old one so that context.foo="data" ends up called context.set('foo', data) instead?

I'm guessing I can use Object.defineProperty for this, but I don't really understand how.

is this for a setter in particular or any setter that might be used on the context object? The latter requires proxies. — Paarth, Sep 20 '16 at 06:19
@Paarth This particular one. I need to handle only one property in the legacy function's signature — Shubham Kanodia, Sep 20 '16 at 06:21

score 0 · Answer 1 · answered Sep 20 '16 at 06:36

Using a setter:

You can use a setter for this:

var wrappedContext = {
    set foo(val) {
        context.set('foo',val);
    }
}

Note: I'm assuming context.foo instead of context.foo.bar because the second part of your question does not quite match the example code.

This will create an object (wrappedContext) that will have a foo property that will call context.set() when you assign a value to it. So then you can do:

legacyLibraryFunction(wrappedContext);

Using a proxy:

Since you're using node 6.6 you can also use a proxy:

var wrappedContext = new Proxy(context,{
  set: function(obj, prop, value) {
    obj.set(prop,value);
  }
});

How do I assign a value using = when a setter is passed?

1 Answers1

Using a setter:

Using a proxy: