StyleSheetArray implementation with Proxy and Reflect

StyleSheetArrayProxy.js

// https://github.com/WICG/construct-stylesheets/issues/45#issuecomment-522879888

'use strict';

function isArrayIndex(string) {
    if (typeof string !== 'string') {
        return false;
    }
    const number = Number(string);
    return Number.isSafeInteger(number)
        && String(number) === string
        && number >= 0;
}

class StyleSheetArray extends Array {
    #updateStyles() {
         /* Do usual updates when style list changes */
    }

    constructor(...args) {
        super(...args);
        return new Proxy(this, {
            defineProperty: (target, prop, descriptor) => {
                try {
                    return Reflect.defineProperty(target, prop, descriptor);
                } finally {
                    if (prop === 'length' || isArrayIndex(prop)) {
                        this.#updateStyles();
                    }
                }
            },

            deleteProperty: (target, prop) => {
                try {
                    return Reflect.deleteProperty(target, prop);
                } finally {
                    if (prop === 'length' || isArrayIndex(prop)) {
                        this.#updateStyles();
                    }
                }
            },
        });
    }
}