value-proxy

A small, proxy-based library for cleaner and safer model traversal.

Quick example

If we have to work with model objects in which any field could be missing/undefined/null, this expression can throw "undefined is not an object" error:

const dogName = model.person.dogs[0].name;

So we have to check each field before using it:

const dogName = model &&
    model.person && 
    model.person.dogs && 
    model.person.dogs.length && 
    model.person.dogs[0].name;

With value-proxy, we can write the same thing like this:

const safeModel = valueProxy(model);
const dogName = safeModel.person.dogs[0].name.$value();

This won't throw any errors, we just get undefined if any of the fields is missing/undefined/null.

Features

• Guards against undefined anywhere in the expression.
• Supports objects and arrays.
• Keeps detailed debug information about where in the expression we got undefined, and what was the last valid value.
• Can inline lodash calls in the chain and keep the logical order of things.

Logging

If for debug reasons, you need to log something out, you can just write $log() anywhere in the chain:

safeModel.person.dogs[0].$log().name.$value();

This will log the value of the "dog" object, and also some extra debug info if it's undefined:

> root.person.dogs[0] = undefined
>     Undefined since: root.person.dogs
>     Last defined value: root.person = { name: "Cat Person", cats: [...] }

Finally, there is an auto-log for automatically logging out this debug info for every undefined expression.

const safeModel = valueProxy(model, { autoLog: true });

safeModel.person.dogs[0].name.$value();
// { name: "Laika", ... }

safeModel.person.dogs[1].name.$value();
// { name: "Belka", ... }

safeModel.person.dogs[2].name.$value();
// root.person.dogs[2].name = undefined
//     Undefined since: root.person.dogs[2]
//     Last defined value: root.person.dogs = [...]

Lodash integration

We can use some lodash methods in the chain too. With a special syntax.

safeModel.person.dogs.$_find({ id: 3 }).name.$value();

Lodash methods start with $_ and you don't need to pass the object/collection because it receives it from the chain. This is more natural, and it keeps the logical order of things.

With lodash, find would be at the beginning, which is kind of inside-out:

_.find(model.person.dogs, { id: 3 }).name;

Notes

Under construction

The library is not complete yet. It's a proof of concept. I have a bunch of other ideas and TODOs.

The only lodash method so far is $_find, but it's only a one-liner to add a new one.

Performance

Since the library is based on Proxy, performance is still an issue. (But it became 25% percent in the last 8 months.)

I think it's acceptable for small/medium use cases, but I don't recommend it for heavily used objects.

Proxy

If you want to learn more about the Proxy, I recommend reading my in depth blog post about it.