Proxy not detecting change on nested array

Question

Module code:

const fs = require('fs');

class database {
    constructor(database, object) {
        typeof database === "object" && (object = database);
        this.file = (typeof database === "string" ? database : 'db') + '.json';
        object && fs.writeFileSync(this.file, JSON.stringify(object));
        this.db = fs.existsSync(this.file) ? JSON.parse(fs.readFileSync(this.file, 'utf-8')) : {};
        return new Proxy(this.db, this)
    }

    set(target, key, value) {
        this.db[key] = value;
        fs.writeFileSync(this.file, JSON.stringify(this.db));
    }

}

module.exports = database;

Example Script:

var db = require('./index.js')
var test = new db();

test.a = []; // Proxy is called here
test.a.push('a'); // It's not called here, despite test.a being set.

I'm expecting the set handler to fire anytime the object is updated, but when pushing to an array inside the object, it doesn't happen. Why is it not firing?

I'm using node v8.1.4. Supposedly all proxy issues were fixed after v6.

Elliot B. · Accepted Answer · 2018-02-08 18:42:01Z

3

Unfortunately, proxies can only observe changes made on the target object -- proxies cannot observe changes to other objects nested on the target.

test and test.a are two separate objects. So while Proxy will invoke set whenever a change is made to test, it will not invoke set whenever a change is made to test.a.

If you'd like to observe changes to an object and all nested children of that object, then you'll want to use a library purpose built for the job.

answered Feb 8, 2018 at 18:42

Elliot B.

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