Array-like custom class in JavaScript

ArrayLike.js

class ArrayLike {
	constructor (...items) {
		if(items.length === 1 && !isNaN(items[0]))
			for(let i = 0; i < items[0]; i++) {
				this[i] = undefined;
			}
		else items.forEach((item, index) => this[index] = item);
		return new Proxy(this, {
			get: (obj, key) => {
				if(key in obj) return obj[key];
				if(key === 'length') return Object.keys(this).length;
			},
			set: (obj, key, value) => obj.key = value
		})
	}

	toString () {
		return `[ ${Object.keys(this).map(x => this[x]).join(', ')} ]`;
	}
}

const { log } = console;

const arr = new ArrayLike(5, 10);
log(arr.length); //-> 2
console.log(arr + arr); //-> [ 5, 10 ][ 5, 10 ]

const arr2 = new ArrayLike(5);
log(arr2.length); //-> 5
log(arr2 + arr2); //-> [ , , , , , ][ , , , , , ]